We're currently using a generic one that we bought for our Volo and it's driving me me mad - slips down whenever we try and put DD in it and just won't stay put. Do the proper Maclaren ones fit better? I know it's nearly spring but I can't stand the hassle any longer!!!
Ours is 5 years old but it didn't fit much better than a generic - the buggy wouldn't fold properly with it and eventually broke the retaining clip and it still seemed to slither about a lot. It was narrower than the generic one too, so more of a faff to put them in unless you unzip it each time. I did like the fact it matched though (ours was a distinctive check pattern) and it had extra poppers at the top so you could make it snug for a little one.
I have a Maclaren footmuff on my Quest and I love it - the buggy folds with it on (and a couple of toys clipped to the harness...). It does sometimes need unzipping to get DS in (if he's being awkward) but usually it doesn't. He looks very cosy in it.
My Mclaren one drives me mad too. It's a black fluffy one and slips too. So I wouldn't have thought buying a Mclaren one would make much difference. Ours is ok if I pull the straps hard through it before I put her in but it slips easily (does that make any sense at all? Probably not!) It's a PITA.