They will be available for free download from my website as soon as we've finished re-building it. I think it'll also be available from Osprey. But posting it on the FB group means I have a group of enthusiasts who care tear it apart and note the things I forgot (there were a couple) before it's unleashed on the general public.
Nothing will be exclusive to the FB group, per se. But they will get early sight of and input into stuff. It's just easier.
EDIT - @eilif - there's a recent review/battle report
here. Also, I did a video demo for Osprey,
here. Should give you an idea of the level of crunch and how it stacks next to other games in the same approximate genre.