Used as a factory option on 50s-60s-70s small bore Brit sports cars (and I guess Brit Ford sedans). Electric actuation. Can be engaged on top or top two gears in OE applications. Questionable torque capacity for American stuff, but if it stays near that price..... if you can figure out a painless way to hook it up and it goes bang, you're not out much more than a bunch of labor. Let us know how it turns out.