Both devices, and other similar ones, plug in between the twist grip and the ECM to make the twist grip more (or less) sensitive. Differences in the boxes have to do with features, such as Bluetooth connectivity and the amount and type of adjustability. I doubt that you would find any functional difference, as they all work the same way and do basically the same thing.
This was a Facebook post by Pedal Commander. A potential customer asked a question, and I answered. Pedal Commander liked my response.
I would contact Pedal Box regarding the failure, under warranty or not, and ask for a replacement. Good companies stand by their products. I had a failed weatherproof plug on my Garmin Zumo, and when I enquired about a replacement part Garmin sent me a refurbished unit no charge even though mine was long out of warranty. They even paid for shipping.