I've used several Tetenal C41 kits and processed a couple of hundred rolls of 120 and 135 with them. It is all nice and easy. Where 1 litre kit states it will do 12 - 16 rolls I've worked each 1 litre kit well past the 30 roll mark.
I sometimes would like to buy in bulk but it is all too confusing. If someone told me product names, codes and an Australian source I'd possibly go that way. I do find being able to consistently buy a Tetenal kit hit and miss. If you see them buy them!