Kinda a mix between a Bicycle and a scooter... I got one the other day. It's not easy to learn but it can go pretty fast, almost 15+ MPH (not sure how many KM/H is that). It does feel like ski-ing when going down hill.
Trikke has never really caught on, most bike shop don't even carry it.
I believe it takes up too much road to power foreward therefore it is diffcult to ride it in a regular road with traffic.
Nevertheless it looks fun to ride in one.