Double Stack/Double Feed is superior to Double Stack/Single Feed, this has been a known good design element of submachine guns for almost 100 years. The weak point in double to single is the taper which is an additional friction point and usually the cause of malfunction in the magazine. This has been an issue in high cyclic rate firearms like submachine guns.
Additional considerations for a dedicated PCC magazine over a Pistol magazine are that a PCC magazine typically has a curve which also aids in reliable feeding, 30+ round straight magazines like in a pistol are also potential for feeding errors. Also, the feed angle on a pistol magazine is an unnatural reload angle to put the round in the correct presentation to the chamber. A dedicated PCC mag has a natural reload angle relative the the presentation of the round.
All that said, I’m sure it will be fine with the JP, they’ve been making a reliable Glock fed platform for a while. I do wish they offered both a Glock and Scorpion mag version though. I’d probably select Glock if I already shot one in competition and Scorpion if I shot anything else.