My younger granddaughter loves them. I bought her one for Christmas 2016 that was a 3-in-1 puzzle. According to the box it was very difficult.....
My Dad used to have quite a collection of jigsaw puzzles, some of which were quite old. Unfortunately, when he died, my brother gave nearly all of them away. Shame because there were some really lovely wooden ones which I loved in my very younger days where the pieces were all shapes (gloves, boots, animals etc). One I did manage to rescue is a huge double-sided crossword puzzle, but I haven't tried it. I haven't anywhere big enough to put it on, and daren't put it together on the floor
The pieces on that are identical (the reverse side pieces are exactly the same as the front side) but the grids and the answers are of course different. Dad was a hardened jigsaw-doer (he worked permanent nights and stayed up Saturday and Sunday nights as he couldn't sleep), but even he never managed to complete it.