I have the two piece Kokatat with Switch-Zip.
I love the separating zipper to allow “relief” at pit stops. I don’t have to take PFD or Spray Skirt off. (Although it is a bit awkward managing zip with all the gear on.) However, having seen women with the chest zip it seems nice to be able to take the top part of the suit off and tie it around the waist, to cool down, and also to do bathroom breaks. I have to take the whole top OFF to cool down. I have yet to have a problem with the zipper leaking. Yes it is fussy but done right I can’t see how it would leak. I don’t feel that it could be done wrong because it just wouldn’t close at all and to finish you have to tighten the twisting lock so it’s pretty fail-safe. I also can wear the pants and top separately. With the Switch-Zip the suit becomes very bulky in the middle. I found there to be a layer which isn’t really needed but I guess it likely is there for a reason. Once everything is on and I’m in my boat it isn’t an issue. But, I can see how in a smaller cockpit it might be.
The neck gasket is personal but I would echo Randy. I think that even if you were to go in your neck is about water level so the amount of water going in is minimal. And the comfort might just be worth it to some. I went for full DRYSUIT because I was planning to do rescue practice etc. , and hope to paddle year round and tend to get cold easily. I have had some irritation with the gasket but have a new bottle of KY to try next time. Any dirt or salt water in there will make the irritation worse so be careful. Mine isn’t too tight and actually feels pretty comfy. That might be due to the fact that the top is ridiculously large on me. This brings me to ….
Sizing with Kokatat. I am a normal size but found issue with their sizing. The pants were tight when the top fit fine. I had to get the next size up and now feel like the top is way too big but the pants are good. I felt the pants were the more important as all the bending that needs to be done.
On a warm day, it is warm inside. I find I sweat a lot. Be sure to wear quick dry layers under it. Generally, on the water it is usually a bit cooler and I haven’t found I overheat.
Go try a few on to feel the difference. I went to Skyview Outdoors and they also help with measurements and sizing and have lots of good advice and thoughts on the subject.
If you have more questions please don’t hesitate to email. If you are the same size you could try mine.