Season the meat cubes generously on all sides with the BBQ dry rub.
Place the seasoned cubes into a 6-quart slow cooker.
Pour the beef broth around the base of the meat.
Cover and cook on the LOW setting for 6 to 7 hours (or HIGH for 3 to 4 hours) until the meat is tender but not falling apart.
In a small bowl, whisk together the BBQ sauce, honey (or brown sugar), and apple cider vinegar.
Drain most of the liquid from the slow cooker, leaving just a splash.
Pour the sauce mixture and melted butter over the meat cubes and toss gently to coat.
Optional: For a true "burnt end" texture, transfer the glazed cubes to a baking sheet and broil for 3-5 minutes until the edges are crispy and caramelized.
Return to the slow cooker to keep warm or serve immediately.
Garnish with fresh green onions.