Do you lot not find that these are vile to have on your teeth? I've used ~3 from a pack of 20 and whilst the results were great I hated having the slimy things sliding around my teeth for 30 mins every morning.
Not sure if they are the same ones? I tried the vivid 30mins ones a while back, and they were awful, they didnt stick down and were slidey like you say.
the 2 hour express ones are totally different though, the plastic is a lot thicker and rigid, like sellotape really, whereas the other ones are more like cling film.
Stuck them on, and they didnt move the whole two hours!

