While I have seen a picture of a separated two piece BHP barrel, there were more instances reported of breakage of the cam lug. FN did it to get better "grain flow" in the breech and lug vs the tube.
I expect Imbel does it because it costs less to make short breech sections and sleeve in the tubes.
I read one Internet Authority to say he shot them until "smoke started coming out the seam."
I had one replaced, not because there was anything wrong with it, but because I was sinking a good deal of money into the gun and a new fitted barrel just seemed right.
Why do Beretta and Perazzi do it on multi kilobuck shotguns, the Monobloc system?