I used Rodinal 1:100 and it worked fine (rotary processing); I found a speed loss of 1/3 stop using Rodinal w/ascorbate (three different films) while curve shapes and development times remained the same.(posted 8089 days ago)For TMX and Acros I just couldn't see much point in adding the ascorbate, even when examining the negs at 30x. While it did significantly improve HP5+ in Rodinal I decided I could "improve" it lots more by just using D-76H 1:3.
Anyway, it dissolves easily so it's no problem to mix on-the-fly.