1. The tool is slowly but surely getting closer to a solid 1.0 release. After being hired to work on it for an open-world multiplayer project, MAPGrid has seen a lot of improvement overall. All of these improvements not specific to open-world will eventually end up in the base version.
2. Buying on Itch.io should give you the exact same version as on the asset store, so no differences there.
3. Most new features will be free with the base package, with exceptions like the Open-World version, which is too structurally different to be compatible, and adds so much that it cost a small upgrade fee, because I have to eat to survive.