Suggestion for the slippery base...
Buy a strip of that adhesive-backed material used on bathtub floors to create a non-skid surface. At the hardware store, you can buy it in a strip as long as you want & in varying widths. This stuff is very handy for a variety of issues involving slippery surfaces. Just cut it to fit, remove the paper backing and stick on.
I also recommend cleaning the Coaster surface with alcohol (and letting it dry) before putting the strip on. Will make sure of a good bond.
Thank you for your video - I just ordered several Coasters that I will place around my office and home. I will also have some of this non-skid stuff available when the Coasters arrive, thanks to your vid. Nicely done!
BTW, until now, I've been using a modified (read: custom bent) wire mesh business card holder. It works well in the landscape position for my X, but not so in portrait - the stand isn't high enough for stability. The X will slip off at the slightest touch or go over backwards. So, I'm really looking forward to getting the Coasters.