I've recently tried giant danios as dithers, and I've lost 2 so far, either to predation or from them jumping into the overflows. The danios seemed to only work temporarily with my festae pair though, when my male got used to his new surroundings he beat the crap out of his mate and I had to put the divider back up. I'm growing out some convicts as well, but time will only tell with them.
In all respect, it also matters what size tank you have and what type of fish you have, as some are more aggressive and more demanding than others.