These are simply large comets hot melt glued on the top of the rocket for added rising effect at launch. You're right, Tom does use either 39 or 39J as his delay comp but that is rather sparse by the time it kicks in. The comets leave a nice big bright tail all the way up.
Thanks for clearing all that up and verifying. Would love to see some videos of your projects if they are available. You have an unfair advantage over us fellow rocketeers of having Rebenklau as a mentor.