What seduced me with Dignan's divided developer was the absence of time and temperature control when doing C-41 at home, without expensive equipment.
I am using the method for quite a while now, but I still have some in-satisfaction about colour shifts, grain, shelf life, etc..
I already tried to solve colour shifts using different recipes for bath B, decreasing or increasing pH. The grain has been always there, no matter how I agitate or not. Shelf life was 1 month for bath A and pictures were becaming weaker and weaker.
Let me remind you of the composition of bath A:
1 g of Sodium Bisulfite
9 g of Sodium Sulfite
11 g CD4
Water to - 1 liter
I couldn't get Sodium Bisulfite, but I read somewhere that Metabisulfite in 1:1 proportion would do the same. So I used 1g/l of Potassium Metabisulfite.
I tried to use more Potassium Metabisulfite, 2g/l, to prolong the shelf live and indeed, it worked. I could use the same batch of bath A during 6 months with little changes that I compensated with longer bath B until 1 hour.
The use of more Potassium Metabisulfite seems to require longer bath B anyway.
The last insight I had about the divided C-41 developer was this one: Why not helping the second bath with a little of bath A in it? This could have as result a better overall development and, who knows, better negatives?
In fact, I started using 20ml/l of bath A in bath B and then increasing to 50ml/l. Yes, better colours and better density of the negatives. And with constant agitation I had much less grain than before.
But, and this could cut to zero the advantages of Dignan 2-bath developer, if we need 50 ml of bath A for each film, after 20 films we spent 1000 ml that would also have developed 20 films without split development.
But no, bath B with 50ml/l of bath A may develop 2, 3 or more films, so making the process very attractive.