I actually have both right now, and I will be keeping the EE and returning the Haven. I'm an active sleeper who ends up off my pad 90% of the time, so I liked the idea of the Haven a lot (plus $170 for a 22oz 20* bag is a pretty decent deal). It works really nicely when you couple it with one of the mummy-sized pads (prolite, etc.), but it loses a lot of its advantages if you're using CCF or something square, since the pads don't integrate as well with the Haven.
The big killer for me was trying to get in and out of the Haven inside of the tent (Contrail, YMMV). I had a really hard time doing it without brushing the walls.
I picked up an EE RevX 20* after that, and I've been happy as a clam. it's a lot easier to deal with, and it gives me the ability to vent a little bit as temps go up.
Depending on your pad/shelter, the Haven could work really well for you, but it's got some decent hassles associated with it.