i was running 3 of these and think they are very good.
the media i was using was substrat pro, ceramic rings and kaldness k1 and just spread them between the 3 trays. i did keep the coarse sponge round the side of the trays though.
i had 1 problem with a motor getting stuck in its turn on cycle and had to have it replaced but hagen sorted it no problem.
i recommend them.