What about 10 rounds, Count?
If you do not turn the magazine in the SRM prior to firing the 4th round, would you need to manually load the first round from the next tube? It's an interesting idea, and certainly more compact than a Saiga with a 20-round drum, but I think that if you need a shotgun for police/combat use, you want a pump-action so you can use special rounds without worry.
A civilian has no need for those special rounds, but I think at that price range, an AR-15 would offer a much better platform than a shotgun. More support for it and a much simpler MOA. If capacity is required, the AR beats the SRM or the Saiga by far, and reloads are easier.
The Kel-Tec I've heard has had some serious QC issues. I do like the look of the UTS-15 - especially if you alternate magazine tubes (no requirement to manually swap at that point) but I still think at that point, an AR would serve better.