I engrave, have a complete GRS setup, with different hand pieces and a microscope. I also use both electric and air powered rotary tools in my shops...... I've not tried this specific adapter/tool, but have tried other, similar ones over the years, and I personally found them to be a waste of money. They barely do what they are described to do, and are never capable of what you expect.
Tool/bit size and shape are always the issue with these type tools. Always a chisel shape, and far too large for anything other then very large "engraving". If you watch the videos in the link you posted, the one with scrolls is on copper, which is very soft, and the scrolls that are being "cut" look horrible.... mostly due to the overly large tool/bit. Where I'm going with that is..... IF you have this type of tool, using the size bits it does, you WILL REQUIRE some type of precision shaper/sharpener for tool bits. Which means in addition, you're going to need something like the GRS Apex sharpener, which is over $1K. About now, you might be thinking..... "I can just sharpen by hand." Trust me, that dog doesn't hunt.
If it's engraving metals you're seeking to do, this tool will only allow for the most rudimentary, and will only allow you to do large "cuts", in large areas. I know it's not likely what you want to hear, but there is simply nothing out there that will even get you into the same ballpark of engraving as actual engraving tools. I suppose it you have $179 your willing to risk, you can give it a go, but based on my experiences.... it'll just disappoint.