dunhammj wrote a review of Outdoor Research AirPurge Dry Compression Sack on June 12, 2012
I have a Mountain Hardware 35/50 Flip sleeping bag (synthetic). The stuff sack my sleeping bag came in is 7"x16". I bought the black 10 L AirPurge and the sleeping bag fits easily and compresses significantly. I have not had any issues with the sleeping bag getting wet after a long rainy hike.
As for a comparison between this and the Sea To Summit eVent, the eVent is lighter but the material of this sack seems stronger to me.