10/10
It is head and shoulders above everything else.
Most instructional material for guitar is basically just a bunch of exercises, which you can get in abundance everywhere, for free (or even make your own!)
When they do discuss technique, it’s heavily opinion-based with very little evidence, “The pros all do this, but NEVER do this, it kills your speed.” “The secret to speed is (forearm rotation) (pick depth) (a certain pick grip) (etc.)”
Basically, it’s usually just some guy teaching you his specific technique, and sometimes teaching it wrong without realizing.
Contrarily, the Primer is refreshing and descriptive. It just examines and describes a bunch of different things about picking, while never making a judgment on the value of these things. It never says what you should or should not do (aside from a few things like stringhopping).