I have OEM, Manticore and PSA. PSA were dirt cheap before the madness, they needed sanded to make them drop free. Sanding involved the rectangular raised portion on the front and near the top of the mag. Sand and test sand and test until you get the desired drop free operation. Just sand the block down as even as you can. I used a random orbital while secured in a vice. 5 mins per mag. The first one is where you learn how much effort is involved. I used a red 120 grit Norton multi surface, made quick work of the spot. By the way, all worked as advertised. The only loading problems I have ever had with my Skorp is with some lead nosed reloads I was using at an indoor range that jammed up hard.
Even the term "drop free" is a misnomer when you are speaking of the Skorp. They will not drop free when the last round hold open is in effect. If you manually lock the bolt open then yes, they will drop free. If not, you got to push the release and strip them out. It does not work like an AR where you push and they drop or you do the Chris Costa flip.