Brandon Mitchell is a run stopping DE that the Falcons hope can play inside. I think this is a good addition. I don't think Mitchell is really going to be a significant challenge to Lavalais at NT, but he offers much better depth than Lake or Herron would.
But his signing may mean Travis Hall won't be back since both players fill a similar niche on the team. Although Mitchell's pass-rushing skills aren't very good, he can still log minutes at DE. So he has the ability to play all 4 DL positions, and I suspect he'll be used in that capacity.
"Vincere scis, Hannibal, victoria uti nescis" -- Maharbal, 216 B.C.E.