After reading this site, I'm actually pretty impressed. This seems to be a breeder who is responsibly trying to create a new breed.
These dogs are being sold as PETS ONLY! All the masos sold are required to be spayed/neutered. The kennel website says they do not sell dogs for breeding because "This breed will take many years to complete, as we want it done right, and we are in no hurry." Also, the masos are sold for much cheaper than the true purebred mastiffs, and come with health guarantees.
If all this is true, than it does seem like the legitimate creation of a new, healthy breed, and not an attempt to cash in with the designer dog fad. I see nothing to argue with.
The only thing I don't like is she does give a shameless plug to designer dogs, and how they're healthier than purebreds. Perhaps careful breeders can make healthy dogs, but sadly, that statement doesn't apply to 95% of the breeders out there.