I looked at the website. They are unquestionable puppy millers. They are doing multiple breedings of dogs with no titles (show or working) health (x-rays for hips/elbows/patellas) or temperament testing. Their price is ridiculously high, and the premise behind breeding low aggression dogs is the hallmark of someone looking to peddle puppies. They make inaccurate comments about their dog's bloodlines "Pure Ruffian", when there's no Ruffian dogs for 4 generations or more.
If finding a dog w/minimal dog aggression is critical for you (which is not unreasonable), I'd either look at another, non-terrier breed, or look for an adult dog that lives w/other dogs.
Hey, I was partly wrong. They have health tested a number of their dogs (9), which does move them up the ladder in my opinion. I would still never consider buying a dog from them, but this does indicate that they are willing to spend some of their money on something very important when breeding.