It looks like the answer to a question nobody asked, but maybe there's a legitimate purpose? What am I missing about this?

I have never seen a review of these, where someones worked.

I would like to examine the extractor design first hand.

These are all good points.  Along with that I'm wondering what intended purpose would be.  There's already cheap 12ga Turkish shotguns in the AR pattern so why a .410 upper?

The reason for a 410 upper is that it can be used on any MIL SPEC AR15 lower. And a lot of European countries don't allow rifles but do allow shotguns, which is why we see a lot of AR style shotguns from Turkey.

I have looked into getting a 410 upper for many years but never bought one. Part of the reason is I prefer using 3" 410 shells which will not work in an AR15 lower.

Part of the feeding problems reported with the 410 uppers is the shells themselves. All shotgun shells are measured when new or after fired. They are not measured when crimped. And not all shotgun shells are the same length when crimped. With the 410 AR magazines, you have to make sure to stick with the brands that are short enough to reliably fit and feed from the magazine.

And with any semi-auto shotgun no matter style, brand, or gauge they can be finicky at first with lower power field loads versus higher powered loads.

Mine hasn't.  I have one but feeding it even with the right length ammo isn't smooth.  Right now it sits with another project AR I have, a .45 ACP AR, in the rack of weapons needing attention.  The problem I'm having is trying to figure out how to fix it.  It's very hit or miss as far as feeding.  So the last time I tried it was difficult trying to eliminate problems, one problem I have is I only have a single magazine, so I can't eliminate the magazine as the problem.  To me this would be the perfect home defense round too, no over penetration but decent knock-down.  In the next couple of months I plan on really trying to get it working, but at the moment my list of things to do is too long.

I have the upper from this thread, and it has worked perfectly through a few hundred rounds. I just bought it because it was different and might be good for varmints and snakes. I only used the shells listed in the thread below.

https://www.ar15.com/forums/ar-15/IFC-410-ARU-Upper/124-732530/

I wonder if the bolt/extension is strong enough to handle a slightly shortened 444 Marlin, with a rifled barrel swap of course.  The 444 runs at 3 times the pressure.
The Saiga-410 platform handles it fine.

Tony Rumore
Tromix