Hello, I see that you have this pen in your range once with a "POM tip" (polyoxymethylene?) and once with a PC tip (polycarbonate?). For the pen with POM tip, you write that it is for "coated surfaces", while the pen with PC is for "uncoated surfaces". I don't understand exactly what kind of coating it should be and whether the difference matters to me. I want to use the pen with an Onyx Boox e-Ink tablet. Which of the two variants do I "need" or would you recommend?