My problem with the mini shells, is the non existent availability of them.
I think I have seen them for sale locally once in the past several years.
I would like to try some, but they seem so rare, I just stick to standard shells.
I'm sure for those inclined, trimming and loading some short shells would be pretty straight forward and wouldn't cost any more to load than any other shell.
You'd just need to use a thick nitro card wad than a regular plastic wad and stack your load on top of it instead.
Or if you don't want to load over the nitro card, perhaps cutting and trimming whatever plastic wad shot cup you are using would work if you feel that you just absolutely must use a plastic wad but that isn't necessary.
If you are loading any kind of shot, you would need an overshot card if you are roll crimping. Whether bird or buck. I personally like the clear overshot cards that ballisticproducts sells for that.