Usage depends on how much the child likes it I guess. I bought a similar type bike but much cheaper from RD1 for my son's 2nd birthday. He is quite tall but still had to put it on the smallest settings and take the seat off for him to ride it. It was recommended for 3 years and up.
However, nearly 2 months on he is tall enough to have the seat on. Initially he would just stand astride the bike and walk along but now he is beginning to coast and get his balance. He rides it everyday and loves it.
One of the great things about it is that right from the start he could get on/off it independently and any falls were not so bad as there are no nasty pedals sticking out.
I think they are fab and am really glad that we bought it.
Hope that helps.