The article covers a lot of ground; what in particular were you interested in?
I haven’t read either Pfaff or Alexander, so I can’t say whether the critique of them was accurate or complete. And I’m neither a prison abolitionist  nor an anarchist, so the arguments assume some things that I’d quibble with.
I must say that it reads to me a lot like the author is a libertarian in anarchist disguise, which makes me automatically suspicious of his conclusions.
Anyway: many of the basic arguments and facts that he presents are good, but some of them make me very suspicious. And, given the libertarian sourcing, I’m not sure if it’s worth devoting too much time to investigating. Typical libertarian arguments tend to be superficially plausible but fundamentally unsound and tedious to debunk.
In particular, I don’t trust his stats on rates of drug admissions to prison. It’s possible that they’re correct, but I wouldn’t be surprised to learn that he’s playing tricks with exactly how he’s defining imprisoned, and/or how he’s defining drug crimes. Accurate-but-misleading is something of a libertarian specialty.
However, there are some things in there that I wouldn’t disagree with at all. Which bits caught your eye?
 I’m not opposed to the idea, but I’m not sure that it would work given current human imperfections. My usual advocacy is for reserving imprisonment as a last resort quarantine for the intolerably dangerous, and making it as humane and rehabilitative as possible. It’s not an issue I’ve focused on, though.