"Smithies don't use the kits."
Oh, yes we most certainly DO.
I prefer the Brownell's for a number of reasons.
First, the quality is there. These are VERY well made bits, and the handles come in several sizes.
Personally, I prefer the "law enforcement" size. The big handle is too big to control for most work, and the "stubby" handle is too short get a proper grip on.
Second, the bits are VERY hard, and if you over stress the screw, the bit is usually what breaks, not an expensive and hard to get gun screw.
Third, they make a very wide assortment of bits in both widths, and thicknesses.
Last, break a bit and Brownell's will replace it FREE. You don't even have to send it in, just email them and they'll send you a replacement.
The single most important and often used gunsmith's tool is a screwdriver, and the Brownell's Magna-Tip has proven itself to me for a good many years.