Just to be clear, I do not own a Umarex Gauntlet; I just saw youtube clips of it disassembled.
When you look closer it looks remarkably like a QB79, and from what I can make out, it is a copy of the QB79 modded for HPA. It looks like Umarex looked at all the mods available for the QB79 and built the rifle to include the most common ones. Provided that the barrel is good, it should be a pretty good, quiet, low-cost, regulated airrifle. If you believe youtube and forums, it is.
For those that haven't paid attention to the QB craze a few years ago, the QB79 is a CO2 powered rifle that can quite easily be converted to high pressure air (HPA) to give a regulated 12 ftp pcp airrifle; the major modification is to replace the 12oz CO2 cylinder with a paintball 13 ci HPA cylinder. Quite a few people spent time, effort and money to convert their QB78/79's to HPA.
Imagine my surprise when I saw this: Using The Umarex Gauntlet With CO2 Power - Part One
Seems like a step backwards to me.