After much thinking, I finally purchased a TSAR yesterday from The Windy City Watch Collector (Windy City Watch Collector: Vintage Watches, Chronometers & Military Timepieces for Sale). I'm now just waiting impatiently for it to arrive!
I'd looked at getting a JSAR at first, but I eventually decided (after trying on a very large TW Steel watch) that a watch with a diameter of 46.6mm would be too big to wear as an everyday watch, plus the TSAR has the added advantage of having tritium illumination.
I've seen that Marathon watches, the GSAR/TSAR/JSAR, being advertised as being used by German, US and Israeli military, but does anyone know which particular units?
I see that some of them have a Nato Stock Number (NSN), although I doubt them to be general issue. They're probably more specific to specialist units.