Didn't seem to be whole lot of info on the GDF-100 when i was looking for one so thought i'd post some info having owned the watch now for a few weeks.
Firstly it looks much much better in the flesh than the stock photo when looking on the web, the red dial in particular is not as bad as it looks!!
Secondly it is a good size a little larger than the Riseman which is the big brother in terms of features but will certainly be fine on wrists of 6.5" or greater.
The display is this watches best thing, you will struggle to find a clearer bigger display!! And you get the time in every single mode something that is in short supply of a lot of G's these days. I hate not seeing the time in Stopwatch / Countdown modes!!
This watch is a doddle to read whether sitting still or hurtling along on your mountain bike!!
Timer mode which is 24hrs but no auto repeat
I have found the readings of the Barometer and Altitude when correctly calibrated to be accurate and having owned the Riseman, Suunto Vector / Core etc....it is just as accurate but lacks the recording features that these models have. The core has a Baro / Alti lock so pressure changes don't effect the altitude when you haven't moved but if you understand how these features work it is fine. The only time the altimeter is truly accurate on any of these watches is when you have just set it and start your walk / hike and update it as you go etc.....I hardly ever used the recording features on the more advanced watches above though, i just wanted to know what the altitude was at a given time and that in a way is what i like about the GDF.....it is simple!!!
It has nothing that is complicated just basic features that you'll love to use.
Good back light that uses two led's that light up the display like a Christmas tree in white light! option of 1-3 sec's. Note no auto illumination on this model probably to save battery!!
Non Tough solar that would have been really nice not to have to worry about a battery at some point!!
I picked mine up for less than £100 so cheaper than a lot of other A/B watches.
In conclusion if solar and atomic are the most important things then this will not be for you, should you however want something you could really bash up without worrying too much about the cost with very clear simple to use features then you could do a lot worse than this!!