On some the latency is within 45-60ms (that's the best I've tested, under pretty strict LAN conditions), but average is more like 100-200ms. Not good enough for gaming, but fine for things like watching video, if you really want to do that.

Most employ heavy compression by default, and it looks a little more pronounced with motion. A few have 'high quality' mode, but especially on the Pi-based KVMs this eats up more CPU, so I don't use that.

It's on the whole best for use cases where you just need to log into remote servers and check on things, or reinstall/re-image something. I don't think I'd like using any of these for a constant remote session for daily work. I do use Screen Sharing on macOS for that sometimes, and it works great in its low-latency mode. None of the KVMs I've tested are quite to that level.