Question........(obviously) I understand in the rules single stabilizer no more than 12" from blah blah blah.............I am shooting a single AEP HC legal stabilizer off the front.
Right now for my local winter league, I also have a SIMS "Stabilizer Enhancer" screwed into the rear stabilizer bushing just for some vibration reduction (heck I don't even know if it's working really), but for those not familiar with this object it is basically simply a threaded SIMS Limbsaver like those that would glue onto your limbs.
It has no weight and offers no stabilization benefit........

IBO legal or not for HC?

I shot one all last year and my equipment was checked by IBO officals. These things are allowed by the rule book. I cant quote the page its on but I have seen it in their. It makes a special reference to a dampining or vibration reduction device. Or maybe Iam just thinking I read it in their. But I do know that if you put one on the front of your stablizer it counts as the total length of your stablizer. Look real hard at the rules its in their somewhere. My equipment was checked very closely at Erie and the enhancer on the back of my riser was never mentioned. If you think those things make you shoot better then they do.