they are super dangerous on road bike. They are slippy and can make big bump at 25mph.
My route in to town from where I live is down a lengthy slope, towards the main station in Bristol.
I can quite honestly roll down there at around 28mph with no pedalling at all. To be fair, it scares the life out of me at times, and i'm pretty hard to scare in general..
Maybe that's the main reason I haven't tried to Dongle my bike to override the imposed pedelec's legal limit as I may become too used to riding 25mph on some flatter roads, (the temptation is still there so...).
The 15.5mph limit is a mothering experience I get cheesed off with sometimes but I'm kind of happily living with the 17mph cut off I get from the Kalkhoff. I think 20mph would be my ideal cut off.