I often have problems with my keyboard sliding around my desk, so I replaced my SteelSeries QCK+ with the MM300, to provide both a quality mouse surface, and a nonskid surface for my keyboard to rest on.
The vertical surface originally looked small, as I was used to a 400mm tall pad, and the MM300, as the name implies, is only 300mm tall. However, I don't miss the extra vertical space at all, and, even with the keyboard taking up a lot of horizontal room, I have just as much, if not more, horizontal space than I did with the other mat. It should be noted, however, that I am largely a MOBA player, and do not play FPS games, so I cannot comment on if the vertical space will affect performance for players of other genres of games.
Appearance-wise, the pad is wonderful. The pad feels good to move your mouse over, providing speed and control, the grips on the bottom feel a lot better engineered than previous pads I have owned, and the stitched edges definitely add to the overall feeling of quality. While I usually get flat black pads, the graphic creates some visual interest, without being too over-the-top ridiculous, and I enjoy how it looks sitting on my desk.
Overall, it's a great mouse pad. If you're having skid issues with your keyboard, and looking for an extended pad to create a gaming surface for all of your peripherals, I would recommend the MM300 in a heartbeat.