The zipper has to be fully seated before starting the zip. That can prove a bit tricky. Once started, though, it goes around and seals very well.
It takes a steady hand.
Once the zipper has come all the way around, the round knob clasps over the nut, then screws down tight to seal the zipper.
Sealing the zipper.
Compared to the more typical front-entry suits, this arrangement gives a smoother chest, and certainly makes "relief" much easier !
The suit has some other well-though-out touches. The hood is removable, secured with three velcro straps that weave under cord around the neck. The hood also has a side-mounted flap that snaps shut to cover the face, or snaps back to open it up. The neck area can open up for venting - not open to the interior of the suit, but essentially a fold of Gore-Tex over Gore-Tex in case of ice buildup. The suit's top and bottom have an extra flap of GoreTex to fold over the zipper, secured with velcro, so that when they are worn separated, the zipper is protected. Self-draining pockets on both arms and one leg complete the cargo layup, although oddly there is no chest pocket, as I've seen on the Expedition and Meridian.
All in all Mr. Cowgirl is happy with the drysuit, in particular the flexibility of SwitchZip - Kokatat already makes a compatible Anorak that zips on to the pants, so for low-risk touring, that might be preferable, in order to let out some heat. The removable hood was a key selling point, as his primary paddlesport is whitewater, where he doesn't want a hood.