We're sort of in transition now...
A has started to roll over in it and get tangled up, so I put her down a couple of times without it and she went to sleep without fuss.
But DP thought we shouldn't ditch it altogether until he has a chance to lower the cot - just in case she manages to pull herself over.
So, Ive been putting the sts on really loose and she is going to sleep fine. She has woken a couple of times at night (she doesn't usually) and DP has gone in and straightened her out and she has gone back to sleep.
So I'm thinking the transition won't be too bad - I'm really relieved and was preparing for the worst.
My friend did it at 10mths and it took 3 weeks - there were some days her DD didn't sleep at all, or fell asleep sitting up in the cot!