[welcome]
From what I've read they are dead quiet, skim a bit wet and are very compact. The amount of air they introduce to the skimmer body and bubble size is very impressive, they just don't have a big reaction chamber as other skimmers.
I'm probably going to get one for my next tank, if interested I would recommend you follow Tunzes own tank size recomendation in accordance with their suggested stocking. It seems as if they have done their homework.
Also they seeem to work best with a moderate to slow flow in the sump, which IMHO will save you lots of problems down the road (bubbles, return pump heat, noise, etc)