I looked into the Edge EZ, and while it's straightforward and simple, I passed. While I don't have a tuner yet, I wouldn't put my money tward a preprogrammed chip. I would just spend the money, and get either a TS, TW, or BD chip. These are adjustable in cab, and a 4 position chip, that is truly custom tuned to "YOUR" mods and setup, is going to be far more effective, and efficient than something that's preprogrammed.
There are a lot of guys here using preprogrammed chips. Some are reburnable, some aren't.
As for wether you can stack an Edge EZ on top of an Edge Evo, I have no idea.