Fenlander - I think JK's probably about right with his assessment - although a sweaty smelly set of waders left in your sib is possibly a good security measure for short trips ashore!
Just to help explain the difference:
Originally Posted by Fenlander
Flotation suit: Not totally waterproof relying on ankle seals. Perhaps too warm on a day that warms up mid trip.
Really not waterproof at all (certainly not for immersion, better ones are to rain) don't think of the ankle cuffs as "seals" they are intended to let water past just slow it down.
Dry trousers without integral "socks": Also not totally waterproof relying on ankle seals. Waist high ones perhaps most stylish choice.
These are designed to be waterproof. User feedback seems to suggest there is some "seepage" but you shouldn't end up with a suit full of water.
Bear in mind that if you are wearing anything long term (i.e. not just launch / recovery) on the boat it will affect buoyancy / effectiveness of Lifejackets to turn you over and so you might need to look at bigger Newtons.