Read the text carefully... All it might do is shorten the life of the disk drives

If you mount it vertically (on end) then you're risking a lot more than that. The tray will sit on the wiring looms at the back of the player and potentially cut through the insulation eventually (so put lots of tape between them) and the rubber shock mounts will almost certainly come out of the tray after a few months, causing the entire disk assembly to float around loose. I know people have been running their players like this and it doesn't necessarily cause problems, but of course it could damage the drives, short out something inside the player, or bring about armageddon.

Rob