Canyon Dancers are great because they provide a tie-down point on your bike. You don't have to worry about trying to tie off a ratchet strap to your fork tubes. They bring the tie downs out past your fairings as well so you're not loading up a piece of plastic with the tension from a ratchet strap.
They slip over each grip so, no, if you've got anything mounted on the end of your bar (hand guards, mirrors, etc.), they won't work unless you remove these items. Bar ends are no problem though.
The strap on them is designed such that as you tighten a ratchet strap on each end, the plastic cups that go over your grips tighten towards the middle of the bike so there's no way that they can slip off.