This looks promising because it looks like it will work seamlessly with tmux/screen, something rvm struggles with.
What problems did you see using rvm with screen? I use that daily and haven't seen any problems so far.
If you switch to JRuby in the first screen, then switch to the second, the changes don't propagate. e.g.:
(first screen)
$ rvm list
rvm rubies
=> jruby-1.6.3 [ darwin-i386-java ]
ree-1.8.7.2001.03 [ x86_64]
(second screen) $ rvm list
rvm rubies
jruby-1.6.3 [ darwin-i386-java ]
=> ree-1.8.7.2001.03 [ x86_64]
It's not a big deal -- you just have to make sure you do the right thing -- but it is unexpected and has burned me a couple of times. It looks like rbenv won't suffer from this problem.