Just bought the SOSF about a month ago, and I just got a message from Euclid asking me about my opinions on both watches since he's thinking of getting one or the other.
Age of U1: about 1.5 years old. SOSF: 1 month+
What can I say but they're both really pretty watches! On comparing the U1 and SOSF, I would break them down into Overall Design, Build Quality, Legibility, Movement, Wearability.
What spoke to me about the U1 was it's clean utilitarian design, strong hands, sand-blasted through and through and a no-nonsense look. It's masculine, and you can definitely see the Germanic design influence. This was my first purchase. Functional design is form in itself. The standard rubber strap is a joy to use, comfortable and secure. I won't reccommend picking up the steel bracelet at the onset, unless you really decide to wear the U1 out on dressier occassions. Give the rubber strap a go, unless you're strictly against that look.
Immaculately polished case and indices, guilloche-effect dial, trademark love-it-or-hate-it Breitling rider tabs on bezel. This watch SCREAMS compared to the strongly stoic U1. The brushed+polished case and bracelet is a good compromise for people who desire a little pull-back from the traditional Breitling "bling". What I like about the SOSF are the applied B-logo, solid bezel, as well as the applied numerals and indices.
Discounting movement and their price ranges, the U1 and the SOSF will appeal differently to you depending on your mood. Due to the applied indices, the SOSF has much brighter lume than the painted on U1. Crown with crown guards at 3 for the SOSF, vs. the less unobtrusive (in keeping with the tool-theme) 4-o'clock position on the U1. Strong Teutonic design elements on the Sinn for the stoic masculine man, vs. the elegance of the gorgeously polished and practically brushed SOSF.
Analogy: if you've watched Terminator 3, the SOSF is the TX, beautiful but every bit as effective, and the U1 is T-1000, traditional stoic design, but just as deadly.
Tegimented special corrosion resistant U-Boot Stahl (specially developed and used by the German Navy) for the bezel, which turns very solidly on a 60-click inset. Crown screws down tightly, threaded so that the "S" logo is always in the right orientation (if mis-orientation bugs you... it does to me!). I've never babied the U1, took it diving, sand-castle building, rock-climbing, cycling, hiking..and thus far, ZERO scratches on the case. Perhaps only one notch down from ceramic cases? Big deployant buckle on the rubber strap is awesome and gives a good counter-balance to the heft of the case. Only drawback is that you have to cut the rubber to size it. Measure twice, cut once! Some users complain that the weight distribution with the steel bracelet is off, so you might want to research more in that area. Steel bracelet (which I have) is solid, with little side-to-side play. Links are screwed in.
Anything over 600m WR is overkill IMHO, so both watches are just as solidly build. Points go to the U1 for the specially aligned threads (small issue for those who don't care, but a pleasant surprise for me), but if you want to wear it exclusively on the OEM steel bracelet, the SOSF trounces the U1 soundly in the comfort and feel of the entire watch on bracelet.
Immensely legible. Large white painted-on lumed hands, white hour indices on a matt deep black dial. Date window next to 3' marker. Takes one glance to tell the time. Pointers (tips) of the minute and seconds hands are exactly the width of the minute/hour indices makes for precise calibration. AR coating on flat sapphire makes the crystal "disappear", though you might have to contend wth smudging issues, which, while distracting, does NOT affect legibility at all. Lume isn't as generous as the SOSF though, so night-time performance suffers. I would say the lume shines about 50% less than the SOSF, sufficient for my needs though. If you work in the dark for extended periods of time, you might want to keep this factor in mind. Otherwise, the U1 is *the* most legible watch for daytime and sporadic twilight use.
The shine factor which makes the SOSF stand out loud and proud tends to be a tad distracting for the user. However, the black dial model (which I own) contrasts perfectly with the hands and indices, so it is still possible to tell the time from a quick glance. The AR coat on the domed sapphire helps when viewing the watch at a tricky angle (such as while riding a bike or driving) but the fact that the sapphire is domed (my favourite) reduces the available viewing angle of the SOSF. Lume is fantastic though, and the glowing lume is apparent immediately when you walk in the shade on a sunny day. Bright light might cause unnecessary or undesirable reflection on the watch though.
A tough decision. The matt finish and big blocky dial on the U1 makes it much more legible than the SOSF under lit conditions, but the painted on lume disappoints when the sun goes down. The attractive finish on the SOSF causes it to be glaring at certain angles, but the SOSF has a thicker lume application and thus it stays lit brighter and longer than the U1.
Workhorse ETA 2824-2. Proven, and reliable. I've had this watch for close to 1.5 years and it started out about 3 secs fast but settled to -1 sec/day now. Variation is consistent, and even after using it in harsh environments like off-road biking, where the watch is subject to vibrations and shocks transferred from terrain to handlebar, accuracy is still dead on. Feels a little rough when winding as compared to the SOSF, but that does not affect the timekeeping ability. Impressive for a non-COSC certified movement.
I've heard lotsa reports of the Breitling modified and finished 2824s being dead accurate, but I'm quite disappointed with mine. It's currently running +5 sec/day, and not as accurate as I had hoped for in a COSC-certified timepiece. It does run within COSC-specs, but when my two other watches, the U1 and Speedmaster (+0 sec/day), which are non-COSC certified, can best this by 4-5 seconds, I am a tad disappointed. Apart from this though, I would expect the SOSF to settle in after a year and hope it keeps better time then.
Nothing to compare really. Both use the same ETA movements, and both can be easily regulated to optimum accuracy. Since both are dive watches, a display back is not an option and thus comparing the finishing on both watches are moot. I have no doubt that both the U1 and SOSF are finished extremely well, and most importantly, both are using proven, reliable, easily serviceable movements.
Strap on, and forget. Honestly, it takes anything you can dish out and keeps on ticking. Versatile looks - sporty on the rubber, dressy on the bracelet, utilitarian on a NATO/ZULU. Be warned though, the bracelet/rubber combo makes this watch too thick to fit under a normal cuffed shirted (NATO is moot for this point.) However, if you have lots of french cuff shirts, they just might be able to accommodate the U1. The watch is immensely heavy, and excellent if you like your watches to have a certain heft. Wears really well on the rubber, but one can feel it having a slight imbalance on the bracelet and even worse on the NATO. If you like the NATO look, I would suggest getting a ZULU instead, as the material is thicker and might make wearing it a tad more comfortable. Some people have problems with getting the right bracelet size though, so be warned about that.
Even more versatile than the U1, looks sporty as well as dressy, depending on your attire. As with the U1, you might find that only french cuffed shirts can accommodate the SOSF. I have it on the bracelet and a Hirsch Carbon Fibre strap. The SOSF on the bracelet is excellent, and the only reason why I wanted it on the CF, is because the CF strap is orange and I really want my SOSF to be my "shout out" piece. However, due to the finishing on the case, you have to be a little more aware of your surroundings in order not to ding or scratch the SOSF.. makes me a little more conscientious about my wrist than when I'm wearing the U1
The U1 on Rubber is very comfortable, whereas it might have some sizing/balancing difficulty with the bracelet. The SOSF is excellent on the original bracelet and a thick padded strap. If you MUST have your watch on a bracelet, I would recommend finding a way to try on the U1 on the bracelet first. You tend to have to be more "careful" when wearing the SOSF as opposed to the U1 since scratches and dings show up on the SOSF, whereas the U1 really is bomb-proof.
Both a divers and both are very well made and designed timepieces that I, and many others the world over, are proud to own. They perform admirably, and are over-engineered for about 99% of the people who own dive watches. However, looks-wise, they're pretty differentiated. I suggest trying both on, as they look different on pictures and on your wrist. Play with the bezel, wind the watch and hang it on yr wrist and feel how it fits. One of them would literally sing out to you. That's the one you'll want to get.