The second was believing what I read in a book about setting (this was when I'd already been setting diamonds for over 20 years and should've known better, but it seemed a good idea at the time) and making the mistake of buying a range of those seating burrs.
I am sorry, but I use your mentioned burs all the time. They last
longer than the edged one. But The speed for using should be very
slow 100-200 Rpm. Use them in a handdril and a drop of oil on them.