Are yours tungsten tipped on the countersink.... The carbitool ones cost me less than that through my supplier but not near 20 bucks...... I get near on 20 000 holes per bit but the countersinks chip in the end so i never sharpen them just get a new one.... It all comes down to whether they clog in the countersink with the hardwood .....This costs a lot of wasted time unpicking them thats why i switched to carbitools they tend to stay clean.... The square drive bits are the pain you never know how many will explode on a job so generally buy them by the dozen to be safe..
cheers utemad