Reagent grade is often only the technical grade that has been tested and certified.
In the past there was a big difference but today in many, if not most cases, the only difference is in the certification. Modern automated manufacturing techniques make for better efficiency to make one batch on one line than to try to make one real good batch and one not so real good batch. For film, go for quality stuff. I used to use Arm and Hammer Washing soda for print developers, It was sort of brownish in the tray but worked fine. However it is common practice, widely done, to do just this.