I’ve used most methods of developing prints, slot processor, open trays, orbital trays, single tray, and rotary drum to name a few. It is oxygen absorption that generally kills developer rather than overuse unless throughput is very high. The stop and fix can be monitored easily I always develop is to completion by timing the process.
Making a 16x12 print, using open trays takes a similar amount of fluids, around 2 litres, to a slot processor, whilst a rotary drum (Jobo 2840) will require about 100ml and a single tray will requires about 750ml.
Time and space need considering here too. If a large throughput in the shortest time is required and the space is available then 3 open trays may be best. If space is restricted then a slot processor will be the best option, but they are expensive unless brought second-hand. If space is restricted and time is not an issue then a single tray followed by a rotary drum will be the cheapest methods in terms of developer used. If the replenishment method is used with a drum then usage is about the same as for a slot processor at about 20ml per fibre paper print through absorption and carryover.
I now settled on the single tray method, it suits me best. I use a water rinse between each of the developing fluids to limit carryover.
Fluids keep best in a slot processor as the air contact is very limited; developer should be good for a month in these and the stop and fix longer. For the tray/drum methods decant the fluids into one litre glass bottles between sessions and use a gas over the developer to exclude as much oxygen as possible. Depending on dilution and make the developer may last a week; to try and push it further is, in my view, uneconomical given the price of wasted time and paper.
I hope that helps.