I would call this a pendant watch rather than a pocket watch. In any case, it's uncommon even amongst tri-compaxes. I can't find another example off-hand, but I'm sure I've seen one before.
My initial thought was that the exhibition back (see-through back) was aftermarket, since UG during that era (almost) never did them. But on a small production run pendant watch, there's maybe a chance it's original (though I don't see a better than average finishing on the movement). I'd like to hear others chime in there.
As for valuing... a lot of people on this forum have become jaded and won't give you a value. Too many people popping on this forum just to ask for free appraisals.
I'd value it at between 2.5k-4.5k. It's not as valuable as a wristwatch variant, even if it's rarer. But there are niche collectors out there.
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