The main reason I would go 9mm is so I can have a cheap, available ammo to shoot and with these derringers I'm not going to go thru much ammo in a range trip. Normally I'd reload ammo, but the primer shortage is still not over. Were it, I would get the .32 barrel.
Thinking more on it tho, I do like loading .38 with two 000 buck pellets and they are definitely effective, as are CCI birdshot. Yeah, I guess the way things are now I'd end up with 3 barrels.
I'm gonna wait tho, given the lower price these Stingers are bound to show up on the used market in high numbers shot very little once people realize how much recoil they have and I don't want to find myself in a Midland Arms situation where more barrels are promised, but never delivered.