It's odd why there are some people struggling to get it working period and others where it doesn't seem to have problems. FWIW, I don't switch my install between up3 and 4.10.1 using jsgme, I've gone down the route of separate installs for each. Seems happier that way rather than using different .exes.
Personally I like up3 and the things it offers and I believe we should continue to support both up3 and 4.10.1 while the devs get the bugs out. If the community doesn't support the devs, enhancements to the game will dry up. Bear in mind we are getting all this though the blood, sweat and tears of a fairly small group of talented individuals, and we're getting it for free!
Jabo