My daughter just got this for her fifth birthday: the Pieceless Puzzle. (She got the "Ages 4 & Up"; I think this one is "Ages 8 & Up")
Check out this video (and enjoy the background music that takes me back to the days of Bob Barker):
The pieceless puzzle is a pretty cool idea! My favorite feature is that you can just grab it and throw it in the drawer for clean-up, and you don't even need to put it back in its box!
The drawback I see is that once you figure out how it goes together, it is then really easy to do. Your brain and fingers remember how the little shapes go together, so it becomes too easy pretty quickly.
The fact that there is an image on both sides helps with this a little.
I should point out, however, that we have this problem with most of our puzzles. They always become too easy after we know them too well. I have thought that there should be puzzle libraries, so you can check out a puzzle, put it together a few times, and return it to the library. That way we wouldn't have boxes of puzzles that no longer challenge us stacked in the cabinet taking up so much space. (But I can't give them away yet, because I have younger children who can use them someday. So the space, it is taken up.)
But I can see why this wouldn't work. Imagine how many pieces would be missing from the library's puzzles!