You can order them on line and some places carry them
Yes that's all I use. They hold up. If you use them correctly. They could lower the price All you are doing is paying for the name.
counter sink is exactly the screw head width. the #10 is the exact width of the #10 screw head.
They're 1/4" hex with a quick-load groove, so you can chuck them into a conventional drill or drill press ... or use the quick-load.
The countersink head can be moved up & down the length of the bit. But, typical of tapered bits, the head doesn't want to center accurately on the fluted & tapered part of the bit ... even with 2 set screws. It also tends to work itself loose.
I have not had this happen yet, but see no reason why you could not switch to a different bit type. set screw works off of shaft size only.
They do okay just don't last long with metal products.