The third thing to consider is ease of cleanliness.  Many machines are designed in such a way as to make them very difficult, if not impossible to keep clean.  Threaded parts, plastic components which scratch easily, airstones, membrane diffusers, hard-angled plumbing and difficult spots to reach can all be havens for biofilm to develop.  If not well cleaned regularly, these areas can be breeding grounds for anaerobic, potentially pathogenic organisms to thrive.  GEOTEA machines are made of food grade stainless steel components which are designed to be easily dis-assembled, cleaned and re-assembled so no biofilm can develop.

The plastic tote, or vessel, is easy to clean and has nice rounded corners that are easy to rinse clean and do not hamper water movement.  If the totes become damaged or scratched over time, they are inexpensive to replace.