Ubisoft are known for promoting their uPlay platform with periodic freebies and the latest in line is For Honor Standard Edition, not the grindy one. The slashing fest is free to keep right now and will be that way until 27 August 2019.
For Honor Standard Edition is the one where you get a few more unlocks compared to the Starter Edition. This is not to say there will be no grinding in the future for the season pass heroes but at least you will have more variety while doing so.
For reference, the Starter Edition is likely the one you have already in case you picked up For Honor for free before but the Standard Edition includes the Marching Fire expansion. If you want to give yourself a headache, you can check out Ubisoft's full of what each edition includes. Here is a vague description of what includes.
According to Ubisoft UK and For Honor Twitter accounts, the promotion will last until 27 August 2019 but Ubisoft US and the official website apparently stated it would go on until 29th. If you intend to pick the freebie out, we would suggest going for it before 27th just to be sure.
Besides, it really is not that hard to add to your library. All you need to do is go to the and log in to your Ubisoft account. The game will be automatically added to your library even if you had Starter Edition before.
While certainly something new and fairly unique on the market, For Honor has struggled in the past to keep its player base.
Still, given that this is a free game, there is no harm in checking it out, especially because there is the singleplayer campaign that doesn't require other players and potentially long queue times for you to enjoy.