I've had no problems at all with my zip seals in a DUI TLS 350 dry suit. I have zips for the neck and wrists. Not a drop has leaked in.
I've made 9 dives with them, so far. The first 7 were with rental suits, and of these, 4 were in suits that were a size too big, because that was all that was available (this might be relavant to posts I've read about wrist leaks). With the correct size (M), the rims of the wrist seals come just short of the heels of my hands. The seals make a tight S-curve, starting at my wrists, going up my forearms, then turning around and going past the rims, then turning back up-arm to the rims. In case it matters, 2 of my dives were walk-ins at a quarry, and the others were off of boats.
I bought my own seals at a LDS before my first rental. There, the DUI expert cut them to fit. I've transferred them from rental to rental and then to my own new TLS 350, being careful each time to ensure they are completely snapped in place. I cut the new seals that shipped with my suit to match exactly the cuts made at the LDS, and I carry these with me to dives as spares in an air-tight plastic bag.
Initially, it was very hard for me to unlatch the seals to remove them from the rental suits. Then I got the idea of using a plastic bicycle tire iron, one that smooth and has no sharp corners. Its flat end works perfectly to open the seals enough for me to poke my finger in the resulting gap and run it around the rim to completely release it. I carry the "iron" in my dive box.
To lubricate the seals for donning the dry suit, I've tried "pure" talc, soapy water, and KY jelly. They all work fine, but the soapy water is hard to carry on a dive boat. The KY is great but if you don't carry a rag to wipe excess off your fingers, you won't be able to pick anything up. Whatever you use, be patient and careful as you work the seals over your head and wrists.
Talc is the standard recommendation (not the scented, chemicalized baby talc), and I'm going to try it some more, despite the white dust everywhere on my suit. It's also been suggested that a thorough dusting of both sides of the seals with talc extends their life in storage. I'll try that this winter.
Hope this is useful.
Safe diving!