"js.b1" gurgled happily, sounding much like they were
saying:

Both of those require REALLY clean - freshly blasted steel to give of
their best.

Indeed, freshly blasted is Sa2, bright mirror is Sa2.5.

You can get Sa2.5 on lightly corroded auto steel with a 3M clean-n-
strip.
An example would be a scrape which has been neglected such that paint
has domed and gone brittle in the surrounding area, underneath you will
find dark millscale which the 3M Clean-n-Strip cleans out to leave
bright shiny metal as a broad crater of limited depth. Then either zinc
product works superbly at stopping corrosion dead - but are mechanically
weak. You need galvanising primer, then normal car paint, but it is
still a weak underlying area.

For this job, they recommended
Rustoleum 769 primer.

Good and that tackles the weakness of pure zinc products (they are meant
for freshly drilled or ground welds on RSJ, where you want the longest
life but also where abrasion resistance is immaterial).

You can buy miniature sand blasting kits; exactly like a paint air
sprayer, plug in to a compressor, will blast small areas for auto repair
etc. Add-ons for pressure washers also exist of course.

Nice to get secondary confirmation...

IYHO, should the Rustoleum be adequate as a one-coat finish on suspension
etc? From what I've read, it appears to be, but...