do not need water cooling, They claim up to 100 holes. The smaller ones seem wear a bit faster than the larger ones. depends on the way you use them and the type of material
I Just bought a RZ5 from David at Tradetiler and used it today for the first time. Cut through grade 5 Porcelain in no time. I then used it to fit shower doors and towel rail mounts and sink holes on walls after tiles were fitted. The 8mm X Core made short work of the dozen or so holes that i drilled; although I did make a small templete from timber to drill within as it can slip and score the tile!! Be warned, as it can turn out to be a time consuming repair otherwise!
Just bumping some of the tiling tool review threads in the main tiling tools forum. Ignore this if it's an old one and not important to you. It'll soon drop off the list.