Interesting idea, but it looks like a pain in the arse to use. I can sort of see his point about focus pullers and line of sight, but the best position to stand is slightly to the side of and behind the lens. This forms a triangle between the focus puller, camera and subject, which gives you much better perception of how the subject is moving than if you were directly behind the camera.
Interesting for sure, but it looks like it's only good for an operator only setup and a shoulder one at that. Seems harder to implement tripod mounted or with any other peripherals like an LCD. Also sort of uncomfortable.
Interesting idea for someone who's willing to hunt for focus in the middle of a shot. Good luck marking that device and hitting them during a pull without buzzing the subject though.
Having said that, I imagine anyone who practices enough with it can make it work.
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