I have the Legion grip module on my previous gen X5. Weight feels great, but I like a super tacky/grippy grip, so I have some Talon sandpaper grips on it.
For me, I can feel a difference, but as most said, it is probably not a necessity. You can play with guide rods and recoil spring weights and master you grip for a lot cheaper, THEN if you must, buy the grip module.
I'm a tinkerer, so I figured I'd play around with the module and see what all the fuss is about! lol