Pro Alt-world levels add an extra twist to the standard picross rules
Alt-world levels are alternative versions of puzzles you've already completed with hints changed to combine the hints of 2 rows or columns adding a new dimension to how you solve the puzzles which can be interesting to players who have already mastered the standard picross rules.
Pro Free to start model has a price cap
Once you have made about $30 worth of purchases of in game currency, the currency becomes free limiting how much the game can cost. This allows you to try the game for free and only put in as much money as you want for how many puzzles you end up playing, while still limiting the total cost to that of an average 3DS game.