I would of just used the Maxxair cover with its supplied brackets that do not disturb the sealant. Especially when taking into account all you had to do was pop out the plugs on the vent housing of the Maxxair fan you have, and attach the brackets provided with the cover. Claiming the screws will come loose over time is just BS.
Airflow? I don't think Maxxair makes it a habit of designing vent covers that restrict the air flow of their fans.
The way that bracket is set in sealant sure looks like a Micky Mouse installation and prone to leak at some point IMHO.
