OK, I just took the time to use the Otis BONE tool today so I thought I'd report back.
I had both a Windham heavy barrel Varmint rifle that I sighted last Saturday and my LMT Defender I shot yesterday to clean. My other AR's hadn't been shot since cleaning and I was going to wait until more of my AR's needed cleaned before trying out the new tool. However, I thought cleaning these rifles now would provide some of you get a little feedback since this thread is in progress. The Windham Weaponry rifle only had about a hundred or so rounds of brass cased ammo through it. The LMT, on the other hand, was super filthy having shot several hundred rounds of both Russian steel case and premium brass case ammo through it.
The Bone tool proved very handy for cleaning the carbon on both the bolts. Much quicker (and a better) job of it than scrapping with a non ferrous tool like the scrapper on the MUT. It also cleaned up the firing pin very quickly.
Neither bolt carriers, however, seemed to have much carbon build up in them so it wasn't a great test of the BONE on them. Maybe the tool didn't really scrap much out by design but it looked like the carbon inside the bolt carriers was pretty minimal on both guns.
Over all, I would recommend this tool to those wanting to save some time cleaning AR's. I had approached buying this tool with a bit of trepitadtion since sometimes things like this are more gimmicks than useful. But since I really hate cleaning guns and I have so many AR's to clean I thought it might be worth a try.
Bottom line---If you want a way to save time cleaning your AR bolt carrier groups this tool is worth it at around $20. Is it necessary? No, but then most things gun related are based upon want rather than need.