I'm good right now with my current "home defense shotgun" which is a Benelli M3 super 90. It is a convertible semi-auto/pump and has enough capacity for my needs. Reloading a shotgun on the fly is easy enough as long as I have extra shells in me. In my current situation I would not normally grab the Benelli if there was going to be a gunfight. I live "rural" with just me and some beagle mixed dogs in the house. If trouble ever visits here it will be met with a .308 caliber M1A rifle.
I agree that a semi auto shotgun has some advantages. It will cycle faster, plus you could possibly still use it if you were disabled. The pump should be more reliable and less of a hassel to clean. Pump guns have a long history in police and military service. I have never been a fan of bullpup designs for rifles, but it seems to me this one is brilliant. With a tactical shotgun, the need for a long sight radius isnot important as for a rfile. The big downside of a shotgun for close quarters combat has always been the length, but this KelTec design looks very short and manueverable. Pluys, it has an intimidating Star Wars look to it. You half expect it to fire a laser blast.
For most civilians rifles have a 16" requirement and shotguns 18" (altho mfgs make them 18½ to allow for variances in production and measurement). Semi's also have the advantage of less recoil than a pump as some of the blowback is used to load the next round. Pumps are cheaper, simpler mechanisms that are generally more reliable as you said, and have the advantage of that distinct sound when you load a round, something that justifiably scares the bad guys and often prevents the need for any further discussion. "Tactical" shotguns often (but not always) have the shorter 18" barrel along with extended magazine tubes to store 6+ rounds of either 2¾" or 3" shotshells. This Kel-Tec has unique dual-magazine tubes and with its 18½" barrel along with the Bullpup design should be exceptionally easy to navigate around corners, in tight situations, etc. I'd give it some time to work out any bugs but seems to be a pretty impressive design.
Rem 870 is the best 12 ga on the planet. You can get it today in a 3-1/2" magnum at Wal-Mart for cheap. I was goose hunting once with a Mossberg leaning in the corner of the blind. I fired my Rem and the Mossberg discharged with no person touching it. I disassembled the gun and threw the parts in the water hundreds of yards apart. I will never own another Mossberg. If you're in your house and you need more than a couple shots (one) with a 12 guage, there's more going on than living happily ever after. If the other person knows you have it, you should not need to discharge it. Plus it makes a nasty mess you don't want to deal with.
Know what would be REALLY sweet? If that was a double barrel pump gun that fired both barrels simultaneously. Talk about a house cleaner (and drywall killer...LOL)