I've seen two. One is a flat scraper and the other you jam into a device and spin it.

 

Is a device essential or does just any good scraper work with elbow grease?

Unnecessary tool.

 

A stiff toothbrush and the cleaner/carbon cutter of your choice is all you need.

Unnecessary tool.

 

A stiff toothbrush and the cleaner/carbon cutter of your choice is all you need.

 

 

this has been my experience as well.. 

While not essential, the CAT M4 tool is the best money I've ever spent. Cleans bolt and carrier quickly and better than I can with a brush. 

I've got the cat m-4 and the Otis bone. My vote goes to the bone as of the three things they both clean, the one that matters most is cleaning the carrier, and it does that better than the m-4. It's also cheaper.

 

Do you need one? No. But it's easier to pack with your gear for the range, and at home it's faster than chemicals and a brush.