I really would avoid those. Unless you have a rack as solid as a..well, seatpost, to couple it to, it's going to wobble and bend about like a bitch - there is a lot of force going through that coupling.
So you may as well just couple it to the seatpost. Trust me, till you get to a hill, you won't know it's there.
A word on geared ones. Sounds like a good idea, but unless you kid/s is a LOT more advanced than mine at 4,5,6,7, they won't have a clue what to do with gears, and it's them wot changes them, not you. Ergo, waste of money. Anyway, you only really need a "boost" up hills, when a SS does just fine as you pretty soon get to the speed where you can feel the benefit.
I really would avoid those. Unless you have a rack as solid as a..well, seatpost, to couple it to, it's going to wobble and bend about like a bitch - there is a lot of force going through that coupling.
So you may as well just couple it to the seatpost. Trust me, till you get to a hill, you won't know it's there.
A word on geared ones. Sounds like a good idea, but unless you kid/s is a LOT more advanced than mine at 4,5,6,7, they won't have a clue what to do with gears, and it's them wot changes them, not you. Ergo, waste of money. Anyway, you only really need a "boost" up hills, when a SS does just fine as you pretty soon get to the speed where you can feel the benefit.