They work just fine on bikes mate and the big advantage is that you need a smaller increase to see a worthwhile gain, 25bhp on a car is nothing but on a bike its noticeable, so the running costs are a lot lower, the bottles tend to be very small though is the downside, so it still doesnt last long.
Most people on bikes DONT have a controller and just use the horn button to introduce the gas at higher rpm only on demand.
The jets would be totally wrong in the ones im getting (well the nitrous one would be fine but the fuel would need changing) but its only 15 quid a pair or so.
Mounting the solenoid somewhere easy to get at to change jets isnt easy either.
Chip