Ok, I have no idea if these work, but looking at the videos, feedback and technical explanation makes it seem possible.
This seller sells controllers which have been modified to fire faster. Instead of using the right trigger in say Call Of Duty 4 for example, you use the new button on the back which simulates more buttons pulls than would be physically possible. Apparently, this is done through the use of a custom microcontroller.
The seller uses all stock photos unfortunately, so we can’t see what the controller actually looks like. Makes me wonder if it is some sort of frankencontroller that looks horribly cobbled together.
No matter what I think though, the seller seems to be doing well. Powerseller status and 99%+ feedback don’t lie. Dropping $140 bucks on one of these shipped seems a little expensive, but I guess a lot of people are more hardcore than me.