The one piece boomstick is still a two piece, it's just fixed because the parts a glued together. The advantage that dye gave to the glue was that it is perfectly centred...but they now say their screw-in ones are just as good. So with a screw one, you can change the backs, but you cant with a glued one.
Glued one is still plenty good-a-barrel, and you can probably get it cheaper too
ok dont get confused by all the waffle
dye barrels ie boomsticks and ultralites have always been 2 peice the only difference is that the older ones were glued and the new ones screw together makeing it poss to swap back sections around to change bore size.
there is no difference in performance between them at all
also it is nearly impossible in the uk to get hold of back sections on their own and if you want to get hold of a barrel with a none standard bore you will more than likely have to special order it