If an open source app asks me to do so, I usually give it a five star review. It's the least I can do to support them and make them visible on Google Play.
But no Google Push Notifications Services, so F-Droid will probably use a bit more energy on apps, because they will have to contact their own servers for notifications. Not a problem if you have notifications disabled tho.
They are more than just playable. They have native versions, because Valve wants to push gaming on Linux. Both are awesome games! I have already played them.
I buy all my games on Steam. It's simply the best, and they support Linux and develop Proton.