I can't get a grasp on Readdle products. Can someone help me out. There's PDF expert, Readdle Docs, and now Remarks. In reading their website it looks like there's about 70% overlap in these products. When does one choose one over the other? Is one more full functioned? Do these products work together like a suite? Can PDF expert manage files like Readle Docs? If I buy Remarks should I then not buy Docs? Does anyone use all these products? I hope their software is better than their marketing.