What makes these different
Boards are generated and checked on our server before you see them. The generator grades a sudoku by the hardest human technique it needs, searches for a minesweeper board that can be finished by deduction alone, and proves that a nonogram or shikaku has exactly one answer. A difficulty level is a property the board was checked to have — not a guess about how hard it looks.
Results are checked on the server against the board it issued, so a solved board is a solved board and a score means the same thing for everybody.
What they do not claim
Getting better at a brain game makes you better at that game. Whether practising one task improves unrelated abilities — "far transfer" — is the most debated question in this field, and the large reviews mostly find that it does not. We say so on every game rather than promising an IQ boost nobody has shown.