I didn't get the stellar results you describe (milkshake cup pattern at 15 yd) - I ended up with a little more than 1/2" spread per yard, which would be about an 8" pattern at 15 yd. I can't fault Vang or his process, though - the gun fired a huge pattern before ("minute of trash can lid"). There's only so much he can do.
Also, they leave the bore just slightly rough with machine marks. They say this slows the wad down for a cleaner muzzle release. There's no such thing as a free lunch, and the price you pay is terrible leading any time you shoot a load not in a plastic shot cup (like a slug).
Here's the first bad word on Vang, then, Dave - whoever worked on my barrel at Vang put a big vise mark on the magazine tube ring, and a nick on the muzzle. Luckily, it's on the outside edge. This keeps the streak going - I've never had a gunsmith who didn't damage something.
Bottom line? If I had it to do over again, I'd spend the money on another barrel, gambling I'd get one that patterned better to begin with, then I might send it to Vang, or I might send it to someone else to have choke tubes installed.