What makes the SA M6 Scout better than the Chiappa? Well other than it's a Chiappa. I've got a Chiappa on the way now, I'm planning on a full strip and getting it flat nickel plated. If it fits under the seat in my side by side, it'll get a trigger lock and spend a lot of time 'stored' there.
#1 Weight.
The Chiappa is just over 1lb heavier - and that's just the base gun, without the adapters. Given that the M6 comes in a a svelte 4.7lbs, and the Chiappa 5.8lbs, that's over a 20% difference in weight. for something that I want for a pack gun (and I suspect a lot of people interested in these are interested for similar reasons), that's a massive, deal killer, right there. Pounds = pain.
#2 Wrong Gauge Shotgun
It's a survival gun. Not a "OMG OMG SHTF AND I NEED A GUN THAT CAN SHOOT EVERY BULLET I MIGHT EVER FIND!!!!" gun. And there's a difference. A survival/pack gun is NOT a defensive firearm (except in dire circumstances), and as a single shot (two shot if you include the .22lr under... Umm... Just don't), it doesn't matter what size of boom you're putting down the pipe - if you get into a gunfight with this, the odds are stacked against you.
But even there, you can get some pretty stiff .410 defensive loads now (Winchester PDX comes to mind.) You don't need a 12 gauge. All a 12 gauge really gets you for this application is larger/heavier shells, so you can carry a lot less of them with you.
A survival gun is a "Feed me until I get the hell out of here or rescued" gun.
.410 and .22lr can feed you. That's the design goal of the gun - always was, even in it's military service. And you can carry a LOT more .410 (about 2&1/2 times as much) for the same space/weight as 12 gauge. Throwing in the .410 chamber insert just adds extra weight to the platform, it just becomes this cyclical "defeats the purpose" situation.
#3 Crap Materials
Specifically that foam butstock insert. What... the... Heck... I've never seen a foam that didn't start flaking and disintegrating after a few years. I don't care what Crappa says about what kind of wonder-material they made it out of... It chips easy. This is a gun that needs to be able to take some knocks. The Crappa doesn't pass the smell test for materials.
Also, the machining and finish quality of the metal is spotty. These guns are known to rust in front of your eyes.
Just those above three things eliminate it from contention, as far as I'm concerned.