It looks like it works well, but I personally think it's a gimmick on any camera really. There is no real need for it IMO. If you are focusing on the head, the eye is going to be in focus.
.
In my experience using the a1 for about three months now, the Bird Eye AF isn't 100% perfect but it's quite good...... Definitely not a gimmick.
I probably shouldn’t be trying to interpret the meaning of another’s opinion. But for me his meaning was likely that Sony invents these more precise functions (BEAF) to entice customers to buy a more advanced camera based on an otherwise small feature like BEAF (when compared to more major improvements). When in fact, having the head in focus encompasses the eye in focus also.
If this BEAF feature vastly improves the speed and accuracy of target acquisition, then perhaps it may appeal to a significant number of alpha shooters and cam prospectors. Personally, I like DoF wider instead of having only the eye in perfect focus while the focus falls off increasing as pixels diverge from the extremely thin focal point/plane, especially at or near the f/1.4-1.8 setting.
I took the poster’s comments (gimmick) to mean just another advanced “selling” feature to nudge customers a bit more, when the GAS bug bites them. I think we all know BEAF can work when conditions are favorable AND when cam settings are conducive to the conditions at hand. But to me, any device or feature that works the majority of the time (51-100%) is a gimmick. When you slide the “ON” lever clockwise, power is supplied to camera 100% of the time, that’s a factual feature, not a gimmick.
[Merriam-Webster Dictionary---
gimmick: a trick or device used to attract business or attention; ie. a marketing gimmick.]
To sell cams beyond your competition, it’s likely prudent to have gimmicky flavors that appeal to the palate of the self-prescribed seeker of cutting-edge technology. And the question I ask myself is, does the extra money justified for these either factual or gimmicky features if they are of little real benefit to my shooting style.