Hello,
Tried both and coming from Siren V2, the Hellvape MD is closer in terms of airflow. The Ares is one step tighter. I alternatively vape both all day long with great pleasure
Building is easy but the MD will definitely accept bigger coils. I put a Quad core micro alien (4*32/38) in it (thank to its desk) without any problems vaping it at 15W... Both are really quiet and smoth. The Ares shows kind of a tiny little whistle on first and second air holes.
When I tried the Ares 2, I thought it could be a great add to the Siren on the really tight MTL side, and the MD being an extent with more complex builds ! thanks
Hope that helps