Wow, I haven't seen those before (or didn't know what I was looking at if I did). I do know that preformed ponds can be difficult to install because it's very hard to get the shape of the underlying hole the same as the shape of the preformed pond, and if it's not right then the water will stress the liner quite a bit when all of its weight starts pressing out on it. For the stepped liners, we used to tell people to set it on the ground and trace around the tiers onto the ground so you knew where to dig. It requires a lot of back and forth, digging out the deepest part so that the next deepest part is on the ground, digging out the next deepest part and then digging the deepest part deeper, etc. With a flexible preformed liner this seems even harder, as it would be even more difficult to see the shape you were digging and leveling, and it seems like the liner would remain floppy and deformed up until it actually had water in it.
Personally it sounds like more trouble than I'd have patience for, but if you do try it, I'd love to hear about it (and see pictures).
