Forced-air register does two things:
1. Covers duct hole prettily.
2. Restricts & directs air flow. (needs may differ for
heating/cooling.)

Overall, forced-air system is designed for some range of air flow,
typically with registers wide open. Any register that can approximate
that should not be a problem.

If you found some that meet 1) and 2) to your satisfaction, durability
should be _forever_ indoors. Unless you slop paint over them often.
Lotsa samples at BigBox and HVAC suppliers to look at; get rec. from
local HVAC folks if you need someone to take chances for you.

HTH,
J