Already picked him up.
Haven't played him though, but apparently he's a little OP.
I'm pretty sure its like the skullgirls thing, where if you download a character within a certain amount of time, you get to keep him permanently.
EDIT : Yeah, it totally is. If you get him during the SEGA free weekend, you own him.
From the store page
The Last Stand Necron Overlord is available for FREE during the Sega Publisher Weekend. Download it now & keep it forever!
blotunga: Nice, though I haven't even had time to play the base game. And i didn't even had a clue that it had so many DLCs. Wtf.
Most of the DLCs are cosmetic or give wargear to make the campaign easier. There's only like 1 that's really worth it, 2 now with the Overlord.