I also think that entrances at both ends encourage a brood nest in the middle and honey on each side. That messes with inspections, and (I would think) makes it harder to keep the brood nest open. It creates a honey barrier on both sides of the nest, and encourages swarming.
My question is about putting the entrance on the long side at one end or the short side at one end.
In one picture I have a short end entrance. There is bee space under the migratory top, so they can move air though easily. I like top entrances especially for long hives, because I question their ease of getting humidity out of the hive without the benefit of the stacked langstroth chimney effect.
The other picture is a long side entrance at one end of a hive I inherited from a friend. It is sideways to the frames which is good for air movement, but is a bottom entrance, which I do not like. However, the hive's top is a peaked roof, which draws air upwards. The second entrance he put at the other end I keep closed, to avoid the double entrance problem.
Since I plan to remove the queen in this hive two weeks before the honey flow, and pack it with capped brood for maximizing the work force, I will open the other entrance to give them access to both ends, but only until they make a new queen.