"Look's good and fixes easily. Should be robust providing you don't have to remove the cowl to often or the locating lugs may break. It's good that fixing holes are concealed but could be a bit wider apart to avoid interference with the vent hole (don't make the vent aperture too big)."
"It is what it is - a plastic vent cover! Made of quite thin ABS; should be durable but I did feel I had to be a bit careful with it when fitting. However, it does make it flexible enough for the cowl to be removed with a gentle squeeze for inspecting and/or fixing duct or whatever without removing the whole fitting. Not much space left for fixings once you've got a 100mm hole thru the wall 'especially if the hole is at an angle as in my case, so take care not to oversize your hole! Perhaps a better design would be fixing tabs on the outside of the frame?"
"This is typical of its type. Built down to its low cost. They are designed to stop back-draughts and water ingress & do this generally well. Where they all fall down is the annoying rattle they produce during gusty weather, and if you have them fitted to your house and maybe the neighbours also do, the cacophony of rattling can be excruciating; especially at night. Unfortunately I dont think there is a quiet option made- what is required is a damping mechanism on the shutter flap hinge and not a useless bit of sponge which is stuck on some models which just produce more bounce of the shutter."