I love 10-frame mediums! Mine have 3 slots cut vertically down the inside of the short ends. These are for hive dividers. The slots are about 1/8" deep, 17/64" wide, and run all the way to the floor, which means the floor board is slotted, too, as is the inner cover. Incidentally, the flip side of my floor boards have two 3/32" square x full length rods attached either side of the hive partitions (the other side is an screened bottom board). These have 3 entrances facing different directions.
The 3-slot medium 10-frame Langstroth hives have lots of uses. With hive partitions in the 2 outside slots, it makes a triple 3-frame mating nucleus box, so the colonies share the heat. This 3x3 triple mating nuc arrangement accommodates more bees than a baby nuc, and gets things started increasing a little faster. It doesn't seem to have as much swarming trouble as baby nucs do.
With a single partition in the middle slot, it makes a 2 x 5-frame double nucleus box. I usually place these over a strong colony separated by a double screen board in the winter for my late summer / fall splits. Again, the small colonies share the heat of the stronger colony.
I make a 7-frame increase nuc by adding a Mann Lake 2-gallon frame feeder, or a 9-frame increaser with a single frame-sized feeder.
I can use 1 partition with queen excluder (queen includer in this case) for isolating a queen on new, empty comb for breeding in a 7-frame open / 3-frame egg laying arrangement. The 3 frames in the queen area are a modification of Jay Smith's method for Cut-Cell Method queen rearing.
It also works for a single medium 10-frame box when everything is going bonkers in the thick of the nectar flow. To this I will add 3 windows in each of the short ends and 1 on each long side to make an observer hive, unless I can build a single, large window with slots in the plex for the short end.
I make the partitions out of 1/4" marine plywood, tall enough to engage the inner covers (3 of them for 3x3 mating nuc arrangement, 2 of them for 2x5 double nuc arrangement), deep enough to engage the slots in the floors, and with little "ears" on them to prevent the bees from sneaking around the 3/8" frame hanger shelves in the tops of the short ends.
The coolest part is any box, any arrangement, any frame. Everything fits, and you can use it for honey-in-the-comb, too. They max out at about 51 lbs, but only when used for honey and filled to perfection (yeah, right! hahaha). You can really grow an apiary with these 3-slot, 10-frame mediums. It seems to me the best of all worlds. The only drawback is cost - that's 3 medium Langstroths = 2 deeps. More frames to build, but I love working in the shop anyways.