I've got that one (the Large size) in both my tanks. There's a number of other people here that use that one too. In general, it's a pretty strong plastic plant, and only a determined adult turtle would be able to bite through it. That being said, Ralph has bitten through it:
You can even see the bite marks:
Frankie has also been able to pull 3 branches off, but they are just friction-fit on to start with, and are much to big to swallow whole.
Also, don't count on it staying stuck to the side or bottom of the tank. I tried that to start, and my guys make it their mission to pop it up. It usually gets unsuctioned within an hour. So I've given up completely trying to make it stick, and just let it float in the tanks.