The extension stores the data into the local storage, indeed. But without beeing someone able to read and use that data by oneself, there is no way to retreive this data, no button "restore form" or some like that.

It does something. You can tell because there's an annoying tell-tale flashes by the scroll bar. But that's the only way you can tell. There's no useful functionality in evidence. No instructions. The forms are not restored, which is the only thing it could be useful for. "Data is saved to local storage", it says. May be true but to all intents and purposes that seems to be write-only storage.