With most any metal process, there's more than one way to skin the cat. The hydraulic dent raiser was designed to be put into use quickly, with no measuring and machining. It's great for the guy with no lathe or the shop that does the occasional dent.
The gauge-plug idea and dent raiser plug set pretty much approach it the same way; drive a plug unter the dent and tap around the dent until it's gone. The issue I see with the commercial gauge-plug is that the nose still should be radiused to prevent carving the inside of the barrel when driven under a dent. Also, having a rod attached to the pin is handy.
Making individual plugs to fit may be difficult for most as measureing the bore accurately and turning the plug accurately is required. Beyond the skills or equipment of most. If you are equipped for it, however, making a plug to fit can be quick. I've made many and can do them in about a half hour start to finish with all the measureing, turning and welding the rod on.
Pick your poison. They all work.
