I haven't seen any seam issues with them. I have seen some boats with patches near the center from what I would consider hard use or abuse. If you are an under 200 lb paddler I'd go with the 9' boat, over 200 and I'd go with the 10'. I am a 350 lb paddler and I fill the large Ugly to it's max. I'f you are concerned with wear on the bottom you might want to buy some material and glue a wear pad on to about 1/3 up the side of the tube.
I've paddled a large Ducky on a few different occasions and they are pretty fun. Stable as Hell, but I really have to paddle to get to where I want to go. I think that has a lot to do with my freak of nature size and weight. If I could talk Matt into making me a fat tube boat or maybe an 11', I think that it would be a good boat for me. I might end up with one yet.
Wishing I was on the river instead of surfing the web...