Aftermarket v's Factory supplied mirrors

Part of a response (by Jan Owen) to one of my earlier post (1.25' v's
2" accessories) was:

I have completely refurbished this scope over the years, adding top
quality mirror cells, exquisite mirrors (primary by Mike Spooner,
certified secondary by Antares).

Is it common for experienced astronomers to change out their perfectly
good "stock" mirrors with "after-market" mirrors strictly for higher
performance? Jan states "top quality... exquisite mirrors." Are
Spooner mirrors better than stock mirrors or just good substitutes when
replacements are necessary; as was her situation?

E.g. swapping a perfectly good Rochester Quadrajet carburetor with a
Holly 750, or, a stock Fender pick-up with a Texas special... Just
curious...

Errol
NOLA