I have them in my sump and its hard to say if they are better or worse than other media. I do have mine all in a big mesh bag, which makes them fairly easy to remove and clean, so maintenance hasn't been much of a consideration.
I will say that I treated my tank with PP 4 times last week (as documented in my "Laying Down - Sick?" thread) and I never lost my cycle or had a mini-cycle. The bioballs are not my only biomedia (also poret foam, matrix, and pond matrix) but I have no plans to remove them.