I am replacing three old toilets (not low flow) in my home with three Toto Drakes. I decided to use the Fernco FTS-3 waxless seals. The local shop had only two in stock so I bought both of them and ordered another one.
For the first bowl, I lightly sanded the area around the horn, vacuumed the debris, and then stuck the first FTS-3 (four barbs on the tube) onto the toilet. I was impressed by how well the adhesive stuck onto the ceramic. I made sure there was a good seal all the way around, and then put liquid soap on the barbs and put the toilet down. I positioned the toilet and put all the shims in, and I was happy. Then I noticed some water leaking out between the rear of the bowl and the floor. I was puzzled, because it was a new toilet that shouldn't have water in it, and I didn't have any water or anything hooked up (the tank was still in the box). I lifted the toilet to investigate.
The toilet came up and the FTS-3 stayed in the drain pipe. It seemed to have caught on some burrs at the top of the drain pipe. The adhesive all stayed on the ceramic, and it came cleanly off the FTS-3.
I removed the FTS-3 from the drain pipe and cleaned it thoroughly with soap and water, and then I dried it with a heat gun (gently but thorough). I tried to re-stick the FTS-3 onto the adhesive that was on the ceramic, but it wouldn't stick that well any more. So I had to pick the adhesive off the ceramic. I took out the second FTS-3, and it had only two barbs on the tube, and the adhesive was not neatly applied to the top of the FTS-3. It was like someone put the adhesive on there by hand from a squeeze tube or something. I put this second FTS-3 onto the toilet and made sure there was a good seal all the way around. It didn't seem to stick as well as the first one. This one had some visible bubbles in the adhesive, which I think were some weak parts.
I investigated the water on the floor and my best guess is that it was water that I somehow missed when I cleaned up after removing the first toilet and/or replacing the braided riser. I dried the floor and put liquid soap onto the FTS-3, and put the toilet down again. This time I was not able to get the FTS-3 to enter the drain pipe. Eventually after fudging around this FTS-3 also came unstuck from the ceramic.
I now have no toilet seals left and have to go shopping again in the morning (it's now 12:48 am). I am guessing that the two-barb FTS-3 is an older revision and Fernco has improved their production line and the four-barb version is newer, but that's just a guess. I am also considering that these seals (this particular model anyway) is a one-shot deal like wax. Maybe in a perfect laboratory environment with a smooth new drain pipe and a level floor that doesn't apply any pressure on the FTS-3 except towards the ceramic, this seal would work perfectly. However, I think if you can place the toilet on the first shot without having to lift it, then the FTS-3 is much better than wax at tolerating some wiggling to insert shims, wiggling to see if the toilet wiggles, etc.. Maybe if there were some sort of gentle force that applied some tension trying to pull the FTS-3 away from the ceramic, it would eventually come off. I don't think it's perfect, but I think it's better than wax. But if your floor is really crooked, or the drain pipe is crooked which would apply sideways force to the FTS-3, maybe wax would be better. I don't know.
I'm just a homeowner, and have installed toilets in the past using wax, and this is the first time I have ever tried these waxless seals. I looked at the Sani Seal and the Fluidmaster and chose the Fernco because I think it's the best design out of the available wax-free seals. I am least confident in the adhesive on the FTS-3. I wish there was something like the FTS-3, except instead of peel-and-stick, you used some sort of cement, like you use to put PVC pipes together. When you use that PVC cement, the resulting pipe fixture seems bulletproof. Something like that to attach the FTS-3 (or FTS-4 etc. depending on the size of the drain pipe) would be so nice to have. It could just come in e.g. a ketchup packet thing in the bag.
Tomorrow morning I am going to go out and buy some more FTS-3 seals, and maybe I'll buy a couple extras. And I'll have to wash the dish soap off the bottom of the ceramic, dry it with a heat gun, and try again. I will try to buy FTS-3 seals that have the four barbs, because I couldn't get the two-barb version to go into the drain pipe (I don't know why).