I've had both tires on my Tundra and I can say for sure the STT PROs are definitely a mud terrain tire and have the noise and rougher on-road ride that would be associated with a MT. I ran them for 12,000 miles and as MT tires typically do, they got louder and rougher more miles I put on my truck. By that 12,000 mile mark, about half the tread was gone, so I estimated I would get about 24,000 miles out of them. This is with regular rotations done at no more than 3,500 miles. The price on them was nice - much less than Toyo MTs I've ran before, but I was also much happier with the Toyo MTs than the STT PROs. I also got about 35,000 miles out of the Toyos.
At that point, I wanted out and sold them to help purchase the BFG KO2s I am currently running. I am totally pleased with these tires - smooth, quiet ride and plenty of traction for everything I have needed. That being said, they are way less aggressive than the STT PROs, so I would have to assume that in some heavy mud, the STT PROs would do better than the KO2s. I currently have about 12,000 miles on the KO2s and I estimate I will get 50,000 miles out of them at the current rate of wear and with rotations only at my oil change interval of 5,000 miles.
To sum it up, the STT PROs are a great, aggressive tire at a nice price, but if I had the cash, I would do the Toyo MTs if I needed a tire that aggressive. But for my current needs (and probably 70-90% of most people), being realistic, the BFG KO2s are where it's at and the price on the BFGs was less than the STT PROs. Of course this is all just my personal opinion so take it for what it's worth.