I always make sure I have an upper entrnace going into winter for these reasons:
o I never have to worry about the bees not having access because of the snow being too deep (unless it gets over the tops of the hives). So I don't have to shovel snow after a snowstorm to open the entrances up.
o I don't have to worry about dead bees clogging the bottom entrance.
o There's not much condensation with a top entrance in the winter.
I prefer ONLY a top entrance (no bottom entrance) all the time because:
o I never have to worry about the bees not having access to the hive because the grass grew too tall. I also don't have to cut the grass in front of the hives. Less work for me.
o I never have to worry about putting mouse guards on or mice getting into the hive.
o I never have to worry about skunks or opossums eating the bees.
o Combined with a SBB I have very good ventilation in the summer.
o I can save money buying (or making) simple migratory style covers. Most of mine are just a piece of 3/4" plywood with shingle shims for spacers. But some are wider notches in inner covers that I already had.
o I can put the hive eight inches lower (because I don't have to worry about mice and skunks) and that makes it easier to put that top super on and get it off when it's full.http://www.bushfarms.com/beeslazy.htm#topentrance
The slatted rack won't actually allow more air in, but it will control the ventilation better and have some more volume of air in the hive. I like them, but they won't provide all your ventilation needs.