Just wanted to say thanks for your mod! I started my first map in Factorio with a lot of mods, this mod included. I then tried a map with vanilla(no mods) just to see the difference, and WOW! I can't imagine Factorio without the biters being so plentiful, and dangerous! This really should be part of vanilla, as an option.
In addition to that, I thought I'd ask about the only concern I have about this mod...
When I set the difficulty to 5 and the max group size to 400(or anything over 200-ish) the aliens move near the edge of my walls, then the front aliens trickle in, and the main group in the back just runs in circles. Without attacking in their full numbers, all at once, the aliens make it too easy to pick them off as they trickle in.
I didn't know if you were aware of this or not, since I haven't seen anyone mention this, so I thought I'd mention it.