I've got one - just the one they had in decathlon - they're all the same as far as I can tell. It's just a telescopic bar with a clip on either end. I bought it for my daughters bike because the crossbar on hers was too short for our rack - the false one was a little higher and so was long rnough. Now daughter has a larger bike I don't think I'll need it (not had it on the rack yet) OHs bike hangs far too low with a false crossbar though (it's a mixte frame and the end of the false bar that connects to the handlebars goes too high up) so I just put hers upside down (i.e. I use the down tube as though it were a crossbar)