Product review (3 stars): I have these.  The birds treat them like the doors on Wild West saloons.
I have an 8-year-old house that has this style of louvered vent.  Four 4" vents and one 6" vent.  The three previous years we had no bird issues.  But now some smaller birds, probably swallows or sparrows, are flitting in and out.  There are little beak- and claw-shaped scrapes on the vents, which were never painted.  This tells me the plastic is pretty soft; maybe the louvers were a deterrent when hard, but now the birds can grip them.

If you have problems with brazen little birds, these vents might not help.  On the other hand, maybe they help until the plastic softens.  So I would recommend painting them, preferably with hard enamel, to protect the plastic so it does not turn soft.

I am pleased enough with these vents that I'll replace with the same things (plus, I am too lazy to rework the mounting surfaces.)  I will paint the replacements with enamel spray paint.  I wonder which the HOA would like more, neon purple or day-glo orange?