I have seen the pyramids, I personally wouldn't use them, though I am not sure there is anything wrong with them.
I usually have someone to feed my fish, I get these small plastic condiment cup and ration out the food (usually with less than I normally feed them) so the person doesn't over feed. I usually start cutting back on what I am feeding them a couple days before I leave to help cut down wastes and I do a water change before I leave, but that is when I am gone for like a week to a month.
If I was just leaving for a couple of days I wouldn't be too worried about it.