they should have the same gearbox software. but that "extra input" means alot
UX1 , for guitars, and dynamic mics only. meaning : MONO Recording only.
UX2 , for condenser mics (phantom power) and if you happen to be recording drums > 5 mics > mixer > stereo input left / right into your UX2. pretty much you can do way more with "2 inputs".
anyway if you're just doing guitar demos and dynamic mic vocal recording, UX1's fine