Brian Nystrom wrote:

Despite Pete's comments to the contrary, I consider a "relief zipper" in
a dry suit to be a must-have item, along with booties and a double
tunnel. I find that the diagonal chest zipper is not positioned properly
to easily be used as a relief zipper ...

Depends on the design.

The diagonal chest zipper *is* well positioned for male relief purposes
on a the MTI Palm Sidewinder drysuit. Picture he
http://theboatpeople.com/atr_riverwear.html#Drysuits

Data point: my Kokatat relief zipper leaks. I know because I paddle
and IK and get a lot of water splashed into my lap.

But I still recommend Kokatat due to their excellent repair service.