well, after waiting for my OH to be ready for us to try the Pop-In (wtf???!!!) we finally road tested it last night!
didn't use the Dri-Night booster because Adam was frankly unimpressed with his shiny new nappy and frustrated with Mummy's fidding about getting it fastened (should have had a practise at a time when he wasn't jonesing for his night-time bottle). so manoevering him into the whole thing plus booster was beyond me. I did add a Little Lamb booster, only had cotton left, and then a LL fleece liner, crossed fingers and sent up a prayer...
(was concerned that if he'd leak through, OH would be even more anti-cloth and insist we go back to disposables overnight. as it is, unless I buy a couple more Pop-Ins or figure out another night-time option, he's going to be in disposables 5 nights out of 7 anyway.)
so, he went in it about 11pm and rather than wait till after breakfast to change him I did it about 8am (as well as wanting to check the results I don't want him to poo in it if poss!). no leaks! whole of the filling is pretty wet but not to bursting point or anything, thnk he could have easily gone a little while longer. just thought - it's a BTP nappy, AE is only 3.5 months, the whole thing + big booster is designed to hold the bladder contents of a 2+ year old, so *should* be ok... thank goodness I was right.
overall, very impressed. thanks for the recommendation!