I love this app. It is easy to use, and the many difficulty levels mean I can choose how much brain-power I want to use. No ads, no ‘challenges’, no distractions. Just a clean, well thought out game with intuitive controls. Free starter packs are great, and the free weekly puzzles make it possible to play for free for a long time. If you play a lot, you can buy packs of the level and size you want.