I'm really uncertain about this free-to-play stuff for next month. I unlocked (yearly sub) and all I'm seeing outside of ESO and some Quake beta are unlocks for "15 days of ESO Plus... Event Tickets, 100 Souls... 50 Shards, 100 Platinum, 2000 Favor" and crap like that. I hate that type of gaming and it's pretty much the reason I do things like buy Humble Monthly where I previously just got to own games and play them without getting milked.
Steam keys have been added for Tiny Echo, Kimmy, Copoka, and Gunmetal Arcadia Zero. HB aren't too good at letting you know about it, I guess, but they should be in your keys library.