Some of the recently published stuff about PPD/Glycin developers is a little misleading. A great resource would be a copy Edmund L. Lowe's book, "What You Want to Know About Developers, Fine Grain and Otherwise", 1939, Camera Craft.
Ansel Adams had high praise for the book.
Anyway, Lowe, who began Edwal, wrote an understandable, clear, and well supported examination of the whole issue of developers. Of particular interest, he detailed the purpose of Edwal 12, and gave suggested methods of using it to achieve different results. The developer is formulated, he wrote, for the typical Chicago conditions: one who took pictures in sunnier conditions were suggested the possibility of lowering the contrast of the developer by reducing the amount of glycin from 5 grams to 2 grams.
He also explained the misunderstood practice of using potassium thiocyanate.
Lowe's book is a snapshot of the apogee of pre WW2 craftsmanship. It provides context for the existence of Harvey's 777 ( a secret formulation derived from the Edwal 12 formula and Lowe's directions ! ).
Either developer makes a splendid developer, using reduced agitation methods, in either a seasoned and replenished system or one-shot.
It is messy: the PPD stains when you spill it. I always pour it in the sink, and have no trouble. And the results are very interesting, and handsome.
Good Luck