Have shot the Aguila mini-shells. They are 1 1/2 inches loaded length.
They will work OK in Winchester 120/1300 guns, but tend to choke Rem 870s. The Rem can be modded to work with these, but I do not recall what it entails, just remember from researching a number of years ago.
Of course, they are just fine in doubles or over and unders.
IIRC, the velocity is about what a standard field load is, and with a slightly lighter payload, the recoil was less. 12 ga mini was still more than a standard 20 gauge as far as recoil.