@ $20 I would buy as many as my wallet would allow after donating plasma and paying whatever bill was supposed to get paid that week next week...
They are kinda a PITA when the majority of people have ball locks when you go to club/homebrew events because the regulator will prob not have pin stuff dedicated to it.
I also think the pin locks are shorter and fatter so you may potentially get fewer kegs int a ?x? area/keggerator/kezzer.
I see used corny kegs sell for $40-60 + shipping online and my LHBS sells them for 79.99 ea. (Yea that is all used and pressure tested.)