I have dived and snorkeled off Cozumel and Playa del Carmen for years now and the reefs there are full of Alantic Blue Tangs. I have witnessed these fish graze for hours on end-I really have! ABT are just the same as a lot of angels and the rest of the tangs-they simply eat all day long-hence the name
grazers 
I see no problems keeping a small fish of this species in a 150gl except for one reason-they might just eat everything in your tank
I think most tangs will however outgrow most systems. So when I keep another tang, I will do what I did with my last Regal, and give it to someone with a larger setup as it outgrows mine.
I have asked many a local fishermen and dive instructors in Mexico why this type of fish along with a few angels to name a few, grow larger than others in there family's. Most replies were that they simply eat anything-even beans and salsa said one fishermen
I too have some great shots of these beautiful fish swimming in huge schools. I will try to post a few-that is if I can get my scanner up and running, as all those pics are 35mm formatt in albums.
cheers, Rich