Not only is this a cool move on Ubisofts part it’s great PR and it almost costs them nothing to allow a game that has long since stopped selling a window of free availability.
Also for all the dumb internet dogpilling this game received, Unity is actually pretty decent and with a solid framerate which was one of the biggest issues it suffered from apart from bugs it should actually be a really fun experience. They introduced a lot of fun elements in Unity that never made it into future AC games when they decided to just make it another bland open world series.
The story is mostly trash even by AC standards but the gameplay was good, the added systems fun and Paris was really spectacular as a playground. You could tell they put a lot of work into recreating that city - and from the moment they announced I thought “man Paris who cares” but it completely won me over.
If you haven’t tried it and like AC I would definitely give it a shot. This isn’t an AC3 situation where it was a pretty bad game with some redeeming elements. Unity is overall a good game if you like AC albeit with a few blemishes here and there.