I have bough 50 mystery potions back when they used to drop AA and PJ, I never got lucky enough to get one of them but I managed to get even getting some ORBs. After orbs where done and Dricken went out of print I gave up, because, if they add DICE to the potion I would try again.
Legendary and Alchemy potions are the best overall, they are really worth it.
Yeah, I had to start buying in bulk so I never missed any days then started getting lucky with prince julian and Mighty Dricken, good luck to you!