It is illegal to breed or sell them for certain, although owning appears to be legal currently. Any dog displaying dangerous behaviour could also have it's owner prosecuted under the 1991 Dangerous Dogs Act.
I did however also find that to own one it must be:
"....micro-chipped, registered and insured, and put on a lead and muzzle in public."
Personally I wouldn't want to be anywhere near it. The barking will simply be a reaction to say "get out of my territory", but a breed like that is much more likely to attack and be able to do serious damage.
OK, there are lots of web sites claiming they are all innocent, but that's like your flatmate pointing a gun at you. The gun is just doing what it was designed to do, but that's not much use to you when you're dead.
Trev