My views, I don't like mouse guards and i don't use them.
Reasons..
1. Early spring pollen can get knocked of while trying to get through the holes.
When they do toilet duties over the winter/spring there restrictive.
I have my inspection boards in all winter and some colonys have a super nadired as a wind break
Entrances are 50mmx8mm some are 25mmx9mm.
Hives are elivated more of the ground for winter to.
I've not had mouse/shrew problems since I've been beeking!
And I've not lost a colony either.
Most of my colonys are 450m and above sea level on a windy hill side.
What works for me, might not work for a beekeeper in the valley.