Nice ! I intented to do something like that but was too lazy ;-) Thanks for doing it and i hope you will forgive my "piggy-backing"
The two heads look very similar from the outside but when dismantled one can see some differences (beside the leds and associated gaskets) :
Pills differences:
- Utorch pill length 11.5mm (left), S2+ pill length 13mm (right)
- Flat front end for the S2+

Reflector differences :
- Utorch reflector length 12.0mm (left), S2+ reflector length 11.6mm (right)
- Utorch led hole 6.5mm, S2+ led hole 7.2mm

One more minor difference : Front O-ring is black for Utorch and Glow-green for S2+
About Utorch quality :
- This is very subjective and i don't have any left with the original Black anodization but i didn't like it like very much ... up to the point that i baked one and sanded the other for a "worn tool" finish.
- An other thing is that one had very gritty threads (ok after several screw_unscrew with added silicon grease)
- The weakest point of the Utorch imho is the driver (no way to remove blinkies)