I have the Gearhead version. I wish I'd gotten the HBI. The gearhead paddle has horizontal serrations that hang onto my thumb as I slide out the mag. The HBI is smooth. Also, my weak hand thumb tends to land on a spot where there is no paddle on the side, exactly where the wings of the HBI releases are. I'm leaning toward the Paddle since I tend to use the wings and I don't want the angle of the Duckbill hooking my thumb.
When using my trigger finger to activate the release, the Gearhead vertical serrations are sharp enough to dig under my fingernail. Not sure if this is the case on the HBI but from the pics they look flatter and the finish looks smoother.
Crap. Now I'm off to spend more money.