The Z817 has not disappointed me at all yet. It's done a pretty good job at tuning mores things than I would have expected it to so I'm happy with mine. They are quite frugal on power too. I have the same Energizer disposable lithium AA batteries in it for over a year now without replacing them. I check the batteries every so often to make there's no corrosion or leaks but that's it. I really want to test the life of rechargeable batteries in the Z817 but the current batteries just won't fail so I'm still waiting.... That being said the only advantage the Z817 has is less weight and it's slightly smaller as the tuning range seems to be about the same. If the weight of the Z100+ doesn't bother you and it's playing well with your rig I'd stick with it for now unless you already have it paired with another rig.