My experience is similarly positive. Like Warwickhunt, I found the KZ’s didn’t fit my ear shape (particularly the left ear for some reason). I’m also successfully using the Sennheiser 100’s coupled with the X-Vive U4 transmitter/receiver setup. As other have said, there is extensive information available on the IEM mega thread here, and I’ll add don’t expect to get your mix right first time out of the box. It takes time to get the eq right on your IEM feed, and the balance across all instruments. But stick with it, the benefits far outweigh the negatives. Playing on a big stage, the ability to wander around taking your mix with you is revelational, and playing small gigs where you are stood on top of your amp crammed in next to the drummer work equally well and you’ll love the lack of tinnitus post-gig.
Currently resisting the urge to splash the cash on custom moulded in-ears and a UHF-based transmitter receiver setup, surely overkill for my needs but my gear sluttery and GAS are a strong persuasive force.