Looking at the ANSI Datasheet, it seems like it's not really suited to the sounds coming from all power tools since they can reach or exceed 110 dBA:

> The Hearing Protection feature is not suitable for protection against extremely loud impulse sounds, such as gunfire, fireworks, or jackhammers, or against sustained sounds louder than 110 dBA.

I suppose if you know your tools operate at 110 dBA or lower levels, you're good to go. The feedback is bizarre though... Hopefully Apple resolves that with a firmware update!

Edit: It looks like it can safely attenuate sound at 110 dBA for 16 to 63 hours. That's impressive!