We have a Happy Nappy as this is what we have to use for our swimming lessons. Supposed to be very reliable, although, despite going swimming every Saturday since last October, Charlotte has not done a single poo in that time
So can't really comment on it, but then it is what the swim school insist on and they should know.
They also do a "Baby Wrap" which is supposed to keep them nice and warm.
Otherwise I can't help you. I wouldn't trust those disposable swim nappies anyway, they are very flimsy and as with normal disps, I doubt they would contain things as well as cloth.