Yes, I had one many moons ago (I think they came out in the 70s or 80s). The pads become uselessly dirty within a lap and a half around the layout. You'll be replacing the pads more often than you change your socks. Good idea on paper, executed with exceptional engineering, but sadly quite impractical.
For me, it will always be a rectangle of Masonite with two nails glued to it, and stuck into holes in an old boxcar.