I know why I like it. The EXP 3.0 reduces the holding power of the clutch by removing one pair of plates, and also tends to increase lever effort. It requires more fiddling with free play adjustment during use, as well.
The Core EXP is a complete "real" racing clutch assembly with auto-clutch functionality, but kind of pricey. It does provide pretty normal feeling lever effort, however, and the adjustments are much more stable than with the 3.0. Both of the EXP types can be temporarily setup to allow bump starts, and then can then be returned their auto-clutch ability on the fly.
The Z-Start Pro cannot be used to bump start the bike under any circumstance. As far as I can tell, that is the only downside to the thing. I find that the Z-Start Pro is more "tunable", more easily tuned, and overall has a smoother and more predictable engagement action than the EXP's, whch IMO makes it more suitable for serious off-road stuff like rocky single track. The lever pull is very light, and if fact, can be almost disturbingly light until you finally figure out that you just don't really need it for very much of anything anymore. The OEM Yamaha friction plates are used, and hold up very well in the clutch on my desert raced '06.
They take some getting used to, and really, they aren't for everyone, but if you like it, you'll love it once you make friends with it.