We keep multiple brittle stars and snails in with multiple Sepia pharaonis and have had no problems with either animal. The tank will still need to be vacuumed occasionally to ensure that waste doesn't accumulate. Shrimp and hermit crabs may help out as well although the introduction of these two species is much more difficult. Brittle stars, and the like, are not a solution to that problem; rather an extra hand (or multiple arms in this case).
Hermits should be no problem with bandensis, but shrimp will get eaten. Brittle stars will do a good job of eating any larger left over food stuff, but it is important to remember that a 'clean up crew' is not a replacement for regular maintenance.
Very true! I hardly have a cleanup crew if any at all. Maybe 1 hermit and a few baby snails. I always felt cleanup crews all have to 'poo' also requiring another system or animal to eat their detritus.
Ive found a good refugium to work great for me. Currently I have a pretty makeshift fuge where the flex tube that I have gravity feeding it loses its siphon once in a while. I know when this happens because my glass will begin to start getting dirty real fast.