I have several dozen of the 11x12’s, a couple dozen 1216’s, and several dozen regular 330’s of various brands. If you just want to know between belisles and 11x12’s, the sauvageau are the meaner tougher, and possibly more elegant beasts for sure, but that’s not how I choose my body grip. They ALL work great. I would say the 1216’s need to be waxed - otherwise they get slow when they rust, but that’s another topic. I choose based on the run size. Fit the trap to the run. A duke 330 works as well as an 11x12 if a beaver swims through either. For underwater beaver, just use the size that fits the run. And if the run is wide enough, by all means put two 330 10”by10” side by side and catch two beaver. Don’t get worked up about brand. If duke made every size I have, and they were cheaper than the other brands of that size, I would run the dukes. Beaver don’t care. And your catch rate will not be significantly different on BEAVER. You will pick up rats in the 11x12’s that are missed with traps that don’t close fully, and that can be both good and bad depending on the situation.
With all of that said, I do appreciate a well made trap like a sauvageau. But I did not spend that kind of money because they catch better, I spent it because in my region the 11x12 size fits the most runs, and no one else makes an 11x12.
And that’s why I no longer have two dozen belisles 330’s. I found little advantage on beaver underwater over a Victor Conibear 330. So I sold the belisles, and when I need a 10x10” 330, I just grab a duke or a victor or a whatever (yes I know duke isn’t a true 10x10, but close enough...) because I’m choosing based on the size I need in that spot, not ability to catch the beaver because they all do that when used properly.