I got several boxes of these from Grizzly a few years go. The ones I
got are a mix of drill bits and burrs, not end-mills. They are designed
to turn 20,000-30,000 rpm with a vacuum to clear out the dust. We have
a DOALL drill press that runs this fast and does a good job of drilling
with the tiny bits.

I have used lots of them to drill out broken taps, etc. Sure they
break, but the price was really cheap a few years ago.

Sometimes handy to have around!

Paul