After trying this product, I am impressed with its efficiency and versatility. It easily fits into any drilling machine and makes countersinking screw holes a breeze. The sharpness of the blade ensures a clean and precise cut every time. The only downside is that it may get dull faster with frequent use, but that's common with most cutting tools.
I read about this last summer while making some Ipe decks. After firing several other sinkers on the same deck. I paid extra for some. One of them has drilled several thousand holes this summer and can still drill finished holes for cabinets this winter. It's worth $25 a bit. PS I had to replace the drill bit after each deck as they tended to burn out during long drilling sessions.