Sorry to confuse in my earlier post! The snug looks like a wetsuit, but with just sleeves, not legs. It looks really really cool, but friends who have tried them say they are a real struggle to get on and off.
The wrap (also known as warm in water) is the neoprene Velcro thingy - much easier to get on and off and really useful in a cooler pool, but they do make baby a bit floaty.
Both options are pricey though, I really recommend that you call the swimming company you've booked with for advice before spending your cash. Some pools that do baby swimming can be as warm as 36 degrees, so nothing would be needed. Additionally many babies grow out of the first size really quickly as they only fit up to 6 months. If you do need wraps, you may be able to get away with borrowing the smaller size from the swimming instructor until your little ones have grown into the bigger size.
The pool we swim at seems to vary in temperature between 31 and 33 degrees, so we only need to use our wrap if the pool is on the cold side.