I agree with Jools on this one - having the neck seal is a great plus, although there are some other products around with just tops that have neck seals.... I'm not even sure if Ravenspring do that too.
The only snag I have had with my Duo drysuit is getting in, and out of it.... it sounds very simple, but, err, I have spent many hrs dancing around on the beach looking like a prize idiot with one arm up in the air, and the other suspiciously down my front not being able to move
I think I finally have it off to a tee though, after managing to get into the complete suit the other afternoon in under 5minutes (a personal record, only after advice from Jools!!). This has however taken over 10 attempts, so practice makes perfect.
The only thing I will say is that these drysuits are not thermally insulated. When we went out with the yacht club a month or so back, I was in my entire drysuit on a wet day, lots of spray, and a cold wind. Only being able to get a t-shirt and fleece jacket on under the top section of the dry suit, I ended up wearing my floatation jacket over the top section of the drysuit as well. I don't know if it had any affect on the way the breathable suit worked, but I was warm, and very dry in the end