My wife and I are both diving 7mm Hendersons right now, without the vest, and we do just fine. We've even used them up in Puget Sound where most folks dive dry all year round. We love these suits. I finally bought a dry suit a few months ago, but except for that, I wouldn't use anything else. The hyperstretch was a godsend to my wife and especially to my daughter (who isn't with us this trip), because they both have an awful time trying to put regular neoprene on. In fact, every time my daughter tries to put a "regular" wetsuit on, she ends up with skinned knuckles. Suit juice, powder, the plastic bag trick, nothing helps. I'm a little more conventional shape so I didn't have that hard a time, but the first time I put my Henderson on I looked at my dive shop guy and said "No way it's that easy." The insulating properties appear to be about the same as anything else, from what we've been able to tell. We keep comfy in them in Monterey waters. That was as true back in January when we were her last as it was last weekend at the Breakwater.
I can't recommend it highly enough. My one small gripe is that it compresses a little funny. Heading down a slope, it doesn't compress as evenly as the other stuff; with mine, there's usually a big change at about 20 feet. But that's easy enough to get used to; it's no different than figuring out the quirks of any new gear.
Recently, we started wearing a 1mm Henderson dive skin under the wetsuit. Not only does it also help with the insulation, but it makes the suit even easier to put on and off. But the dive skin is gravy; the real star of the show is the suit. My recommendation: GO FOR IT!!!!!
That's my totally unbiased opinion
