UFSv2 has more stainless steel parts and it comes with the new top cap so you can use your own drip tip. The UFSv2 also came with a clear window and a SS window from suppliers.
The UFSv1 comes with a delrin mouthpiece instead and a atomizer extender. Plus the UFSv1 has a nickel plated connector and only came with a clear window.
They both work flawlessly and I would purchase either one. If you purchase a v1 with mouthpiece you can always
buy the new top cap to use your own drip tips. And if you
buy a v2 you can always
buy a mouthpiece so it looks like a v1. Get it

?