"More recent, well-designed research reports no improvements in cholesterol levels. In fact, small increases in "bad cholesterol" (low-density lipoprotein) are suggested."
It sounds like it may be a waste of money. Though, I don't know how much it costs.
edit: If you do try it, try not to alter anything else about your diet or routine, so you'll know whether the guggul is making a difference. Though, I'm assuming you'd stop taking the inositiol hexaniacinate. If your cholesterol goes up, you won't know for sure if the guggul is ineffective or just less effective.