Used them on hols, no doubt at all they are very rapid and a lot of fun. Having seen many "playing" in the wakes of ferries coming out of Poole it takes some skill to ride properly and stay on, its not just about going quick in a straight line! Personally speaking though I dont think it would keep me entertained for a long time, its not like you can go anywhere on them given the limited amount of fuel you can carry.
Before you invest have you considered having a ride on the back of a motorbike? They'll probably cost as much to buy & maintain but at least you can go somewhere on them and see different places, as opposed to the same bit of coastline with the jet ski. Plus you dont have to drive anywhere to use a motorbike, its right there waiting for you at home!!