I'll be honest when we first saw these we thought they were a bit of a gimmick. But having tried one out it's a first class product.
Basically you've got a tough waterproof changing mat, get out of the suit, pull the string and you've got a waterproof wetsuit bag.
If you do the sums the mat costs just £14.99 - your winter wetsuit probably cost more than £200 - so do you really want to be treading it into the gravel at the local car park? Highly recommended...