Coincidentally, just last night I was poking around the internet on Ansco 130 and glycin. Silvergrain says that glycine is just an old fashioned precursor molecule on the road to Metol!
http://silvergrain.org/wiki/Glycin
"Glycin once was a popular developing agent, and for this reason, it's described with very favorable words in old literature. They are also blindly cut and pasted in some darkroom cookbook literatures. However, the reality is that glycin disappeared from mainstream because Metol was superior developing agent. Glycin is "chemically weakened Metol." At least in early age of Metol production, Metol was manufactured from glycin by decarboxylation (removal of -COOH at the right end of the picture above). That is, they used to make Metol out of glycin because of Metol's superiority. (In that sense, it is probably better to call Metol a "chemically disinhibited glycin.") That is, the photographic characteristics of glycin and Metol can be matched rather easily by adjusting the quantity, pH and other usual variables of developer formulation. MQ developers with different M-to-Q ratios and different pH could cover a very wide range of developer needs.
Therefore, using glycin is literally reinventing inferior wheels."
Note: I've never used glycin. I'm only reporting this interesting chemistry point of view.