Dave Baker wrote:

I use Draper spanners and sockets quite happily for professional
engine building use.

That's because engine building is easy. New, clean components that fit
together. You care about measuring instruments and torque wrenches, but
wrenches and sockets themselves aren't asked to do all that much.

Now try working on restoring old boat engines, where the part is 80
years old, spent all its working life in salty mud, and is
irreplaceble. Now _that's_ when the properly sized and shaped Snap-on
6 point flank drive pays for itself.