Darda bump n go cars?

[KrisM]

I asked about these at my local toy store today, because they do carry Darda stuff. He told me that all the cars can be used as bump n go, but none work well. He got one to wind up and not go for me, but it did look difficult to do.

Anyone know if this is typical? Or if I buy a car labeled as bump n go will it work well?