Coldfinger,
Water does enter between the two shells. A "sail" effect is not a problem as my BC keeps the upper torso "compressed" and the waist belt and ankle straps (comes with the suit) eliminate the effect in the lower torso. I cannot think of any difference in the drag between the Mobby's suit and the Body Glove wet suit I used in Hawaii.
I only separate the velcro on the back to allow for water to rinse the inside of the outer shell and the outside of the inner shell. (hope that is not too confusing of a description) My rinse process is hang up the suit with a suit hanger, then hose down the outer shell, water down the neck of the outer shell, water down the back at the zipper, water down each arm, water down each pocket, repeat. About once every month or so, I seal up the wrists and neck and put the whole thing in a dunk tank with suit soap. I have washed the inside two or three times but only because it seems like the thing to do. I have not owned another suit, but I think it is reasonable to assume a single shell would not have the same rinse process.
Again, not having owned another suit, I can't say if it is heavier. I never gave the weight much thought until reading some of the other posts. I guess I am just use to the suit now so the weight is not a problem to me.
Someone else asked about insulation with the Mobby's. There is none. You definitely need a liner. I know this from first hand error. I did a dive with sweats only. Puget sound is cold
.
My first post seems to be the only negative one so far. Like I mentioned, the main reason I want a new suit is the shrinkage. I have not asked it anyone else has had this problem nor have I asked Mobby's about it.
In fairness I will say I have never been concerned about the performance of the suit during a dive and never had any problems underwater. It functions as advertised and WITH my liner has kept me warm in the Northwest waters.
As others have mentioned throughout the board for any equipment, see if you can do a demo dive with the different ones. I plan to do this when I start activly looking for a new suit.