I picked up a 3-pack at HF the other day and I must say I'm impressed. I was surprised at how fast I removed the trunion rivets - took less time than I had ever done in the past! Just center punch the top of the rivet and drill. It dug through the rivets in no time and took only one pass. In the past I balked at these things, and used my index bits to step up size by size until the hole was done. I'm going to use this on my next 80% blank build. The trick to using these is to make sure the hole is centered and you're set! You can easily "walk" the bit if you are off-center because the sucker is so thick, you won't have to worry about breaking the bit!
I see the 3-pack is now discontinued, but it was on sale at my local HF for $15 and had all three sizes. This is now on my "must buy" list - strongly recommended to try it!
I like this so much that I'm going to pick up a few spares. This is the HSS version, but that 3-pack has a TiN-coated version, which I prefer for gun work: