I don't know any other web jigsaw sites, so I can only compare it to F2P Pixel Puzzles Ultimate, that I play regularly (88h clocked so far on Steam).
Even though PPU is much more sophisticated (option to rotate pieces, uneven cut, additional microgames inside some puzzles), Jigidi also has at least 1 advantage over it (possibility to assemble parts of the puzzle out of the main board). PPU works almost flawlessly, but lately Jigidi was finally able to polish up it's HTML-5 version, so also no complains here.
On my 21.5" Benq GW2265 solving up to 150-180 pieces or so I find both of them equally enjoyable. With more pieces I'm running into the issue with managing the unplaced tiles, when using Jigidi. 250 piece jigsaws are still OK with me on Jigidi, but I would certainly prefer to solve those in PPU. 600-1400 piece puzzles, that I often enjoy in PPU, I would not even try to solve with Jigidi. Probably 300 pieces is the highest acceptable for me limit for Jigidi.
