Disclaimer: maybe good product for photographers who doesn't need a plate underneath, but for filmmakers/videographers who need to attach a plate underneath, I find it out to switch batteries without hassle.
My opinion: not the best for HDSLR users for video/film.
here is the website
very cheap, but gotta pay shipping and have to wait for 3 weeks to arrive.
Personally I don't find it too useful.
I thought it would by watching my fellow photog using, but not for me who switches batteries every hour or two with very short amount of time given.
I am selling mine now.
Let me know if you are interested.
$4 each plus shipping.