Zantai laid out the criteria in this thread a little while ago.
"With the next patch impacting Crucible and Forgotten Gods on the way, this is your opportunity to check out the content early and be a part of GD development.
If you are interested in joining this wave of new Praetorians, please PM me on the forum with some info:
- Your experience with the Crucible
- Your experience with Grim Dawn and various builds
- Why you think you would make a good addition to the playtester team
Do note that we are very much on the look out for players that make a positive contribution to this community. So if you just joined the forum, this will not necessarily rule you out, but it will impact your chances."
"Just remember: being a positive contribution to this community is a strong motivator for why we recruit a particular player, not just time played or how quickly you can beat Ravager. The way you present your criticisms is also just as important. Constructive posts that try to be objective without sass (ok, maybe little sass) go a long way!"
https://forums.crateentertainment.com/t/playtester-ranks-expanding/45149That was the one and, so far, only time they've invited people to apply. Usually they just do it internally to come up with people to invite. That's how it worked for me. First I knew about it was when I got a PM from Zantai inviting me to join the group.
I assume we get to keep our copies of the game after all the playtesting is finished, but since it's still ongoing can't say for sure. I have my GOG version anyway so if I lose the Steam one I'm not worried.