Alpha- Maybe Jordy will invent something really different? With the conventional silver B&W films I've not had real problems mixing brands. It is just that some developers are formulated for different things; fine grain, high acuteness, long shelf life, etc. And when crossing across brand lines (Kodak developer with Ilford film) it is sometimes not always documented what the resuts will be. Within a manufacturer, the data sheets are usually pretty good at giving the right dilutions, times, and temperatures. Something like D-76 or HC-110 is pretty general purpose for a wide range of films. This process is really pretty forgiving, and you can get really nice results. I've not had experience with developing the dye cloud chromatogenic (C41) films. I imagine it is much less forgiving. My guess is the quality control at the local Jiffy-Mart would be better than you could do at home, but this is only a guess so don't take it too seriously.