It does seem to grip the rails well enough and I dont think there is any issue with them staying on although havent yet used with full roof box. This one was the winner. I have the heavy stainless steel IWatch and with the rubber insert it holds the watch level and keeps the watch in nightime/bedroom clock mode. I put them on both big toes for a 3. This is definitely a less cost alternative option for AirPod. I have large calves (16 in) so I was a little worried theyd be tight but theyre short enough to not matter at all, and Id even be able to wear thick socks or even leg warmers with them. Complete size. But then they are still new. Someone must have tried on and returned. Have two of these in black, so for a change I got the navy color.