They ride well and I think you will likely enjoy the bike. The UOs had a funky shifter set up, with a braze on on only one side. Simplex had a clamp that worked with this. Since yous is gone, I'd just find a Simplex ratcheting clamp on and go from there. There was only one braze on so they could adapt the same frame set to different models, more in the Euro market than in the US. That's my best guess anyway. They're really fun bikes to tinker with, as you don't have to worry about them much and the frame is a sturdy base.
Here are mine, first a UO8, heavily re-worked:
and a Peugeot PE41, a UO variant from Yurup:
Probably your biggest concern will be bottom bracket work arounds, but VO sells french thread bottom brackets, so you should be fine.
Have fun both wrenching and riding!