I just bought a KSG a few weeks ago.
The working parts of the gun are heavy steel, with a good glass fiber bearing nylon based plastic used for the non-critical stock and forearm parts.
It's a good, solid feeling gun with none of the cheesy lightweight feel I expected or any soft, fragile feeling plastic.
I've done a 100% strip except for the magazine tubes and everything is well thought out and very well built from quality materials.
NOTE: I strongly recommend NOT attempting to disassemble the trigger unit.
Even for an experienced person this is a bear to get back together and I suspect that Kel-Tec use a special holding fixture to position and hold the parts during assembly.
There is video online showing disassembly, but note that there doesn't seem to be any on RE-assembly. There's a reason for that.
In any case, there's really no reason to disassemble the trigger unit since trigger pull is entirely suitable for this type of shotgun
As with many new guns it can benefit from a "fluff and buff" of a few key areas and some good grease on some parts to ease friction.
You can get the same effect from just using the gun.
With either the gun smooths up very well and becomes much easier to operate effectively.
As one person commented, don't look at the KSG as a switch-magazine shotgun, look at it like a 7 round pump gun with the worlds fastest reload.
Switching back and forth of the magazines isn't practical because unless you practice like a SEAL you're going to get some confusion between the mags and what's in the chamber and make a mistake.
Plus, if you need a shell from the other mag, you're going to have to dump the good round that's in the chamber, loosing it.
In short, shoot the one magazine until empty, then flip the switch to feed the other magazine.
For accessories, one very popular one is an extended switch to change from one magazine tube to the other.
I looked at those but because they stick out so far from the bottom of the receiver, I'd be worried that a bump could easily catch it and break it off.
Good accessories are the various hand stops like the excellent Magpul and the Magpul vertical front grip.
Unlike many other grips, the Magpul spreads the load over a wider area and lightens the stress on the lower plastic rail.
Kel-Tec states that they've upgraded the lower rail area to prevent breaking it off like happened with an early gun.
An excellent accessory is the Kel-Tec extra thick recoil pad. This reduces felt recoil much better then the standard pad that comes on the gun.
https://www.keltecweapons.com/shotguns/ksg
In looking at the KSG and the DP-12 it's apparent that the same people have a hand in both guns, even though they're made by two different companies.
The designs are both take-offs of the Ithaca Model 37 and both share at lease a couple of parts. The double magazine design is the same on both with very minor differences in some parts.
Reading the owner's manuals shows that some areas have exactly the same words in both manuals, indicating that they were written by the same people.
I'm not clear what the relationship is, but it's fairly obvious there is one.
The KSG is in use with apparently some prison Response Teams, is in use with a South Korean Special ops unit, and I wouldn't be the slightest surprised if you'd find the KSG in most American Special Ops armories.
No military or law enforcement unit is going to buy a junk gun, so the KSG has arrived as a quality shotgun.
People talk about "Gen 1, and Gen 2" KSG's but Kel-Tec says there are no Generations. They simply added corrections and upgrades to the production as they became available.
Whatever, the current KSG has solved all the early problems.
With that said, the major issue with the KSG, and all other bullpup pump shotguns is is operator induced stoppages: Short stroking.
Due to the very short length, the pump handle is so close to the body it's easy to short stroke it and cause a failure to feed.
The shell release into the receiver happens in the very last 1/4 inch of the pump handle's movement and it may feel like the handle is all the way to the rear when it's not, resulting in a failure to feed.
There is some slight resistance to overcome in order to pull the handle all the way back to feed the next round.
A lesser operator issue is failing to push the handle all the way forward.
The next shell in the magazine is staged to move to the feed position when the handle is pushed the last 1/4 inch forward.
What you see on the videos is people trying to run the gun just as fast as possible and causing short stroking or starting the handle back before it's pushed all the way forward to stage the next shell.
There is some resistance on both strokes in the last 1/4 inch of movement and until you get used to the feel, it's easy to mistake the resistance as full movement.
Many people recommend operating the gun as hard as you can pump it back and forth, but all that's needed is a firm pull all the way to the rear and all the way to the front.
If you do some slower practice before attempting to make it sound like a full-auto weapon you'll quickly get the feel and can speed up.
In most cases, firing a shotgun as fast as the videos attempt is seldom necessary and can cause operator induced failures.
In my opinion and admittedly short term experience, the KSG is a quality, reliable gun when operated correctly.
It uses quality materials, and an interesting design solution to the use of double magazine tubes and a bullpup design.