I have ~65 Z-Wave devices around my house, and I definitely notice lag from time to time. Recent versions of Z-Wave seem to be significantly faster and I've noticed it less.

I can't say I _love_ dealing with Z-Wave. But I do like having a single protocol throughout my house. At the very least, any issues I have tend to be consistent. I'd say in this past 6-months, I've practically had zero problems. I blame that overall improvement on ZwaveJs, because some of these devices are at least 5 years old and they're just cranking away without issue right along side my more recent Zooz and Inovelli devices.

That said, I've been strongly considering multiple Z-wave hubs, each running zwave2mqtt with a central mqtt server just to keep everything as fast as possible.