I bought Metallica Premium - reason: physical ball lock & colour changing GI lightshow.
I bought KISS Premium - reason: physical ball lock & colour changing GI lightshow.
I bought Maiden Premium - reason: physical ball lock & colour changing GI lightshow.
I love both of these add ons and that's the reason I prefer Prmium over Pro for these.
I also had ACDC PRO and then went Premium because it has a significant better lightshow than the Pro. Mainly because of the colour changing GI again but also the lit up train and the lit up flames on the right ramp.
Light show is my main factor when it comes to choose between Pro or Premium. And if the ball lock is physical I go that direction too. I find it way more satisfying to lock that ball physically rather than virtual.