The yellow box dosn't have to be mounted underneath the car on the trans. Mine mountes in my kick panel.

 

It "can" be mounted in the kick panel, but the directions don't show how to do it that way, and the manufacturer doesn't recommend it.

The Yellow Jacket comes with instructions on how to mount it inside the car, it can be adjusted on the fly, and it costs less. There are no downsides to the Yellow Jacket if you are looking to buy.

If you already have a Yellow Box you can keep running it until it fails, like mine did.