The fun of UNION BUST comes in the man behind Jethro, who turns out to be Nuihc (!), Chiun's nephew whom the old Korean trained in the days before he hooked up with Remo. Not quite an evil twin, but Murphy and Sapir seem to be taking a swipe at the old "enemy from the past" chestnut. I'm still not completely sold on the violence that often leaves innocent bystanders just as dead as the bad guys; Smith orders the assassination of an innocent physician he recruited to save Remo's life, in order to protect CURE's identity. It's a tricky tone that the authors are shooting for. It's more than action with a dash of humor, but not exactly action/comedy either. The Destroyer books definitely stand out from the novels they're spoofing, such as the Executioner and Penetrator series, which are played dead serious.
UNION BUST is entertainingly written, but an acquired taste. Considering the enormous number of Destroyer books written over the decades, the franchise is certainly more than just a cult favorite though.