I have the Trixie level 3 puzzle! My dog has mostly gotten the hang of it, still working on figuring out the direction of the sliders with her paws (these puzzles are a little easier if your dog naturally uses their muzzle, mine is all paws).
I introduced all the steps to her in waves over a few days.
It’s not meant to be used the same way the other puzzle toys are used for meals, this is definitely something you’re meant to do with your dog, and at least to supervise once they’ve gotten the hang of it. It’s still mentally stimulating for her, we play a few rounds each time we do it, and I rearrange the sliders and cones. It’s not an everyday toy, but it’s good to see her mind at work.