Hi Massimo,
As it happens I own, use and love my SIAB. There is a learing curve that varies from machine to machine, but if you're willing to leave the familiar comfort zone for a littlle while, then your new multi-tracker will become as familar as your current machine.
One reason these units take a little while to learn is they have SO MUCH capability! My Fostex VF160 is very intuitive, and yet it has tons of features I haven't even begun to crack. But right now it's doing all I ask, every time, and doing it well. Laying down tracks, mixing down, etc. can be learned very quickly.
All machines have their own idiosyncrasies, but you learn to love them (thereby making the prospect of changing more difficult). People swear by the Yamahas, and in time, you probably will too.