Well, that free one you posted was updated last year, only supports ox inventory(this one supports all mainstream inventories that utilize metadata), and it’s existence seems irrelevant to this sales post(Unless you go on every paid post that has free variations and make a comment like this one).
It’s $10, open source, and I purchased it simply for its metadata related functions across all inventories as it was worth the $10 for the time it will save me in the future.