I have done training that mirrors a micro ring (though I can't see a gym actually wasting space on one of these). Two of the most effective were:
King of the Square:
The mats at my gym are in squares. We pick a square that's probably around 8x8, so the same as that micro ring (which has a fight space of 9x9). You're not allowed to leave the square for the duration of the drill (usually 2 minutes), and the goal is to be in the center of the square more than your opponent. It helps you to work on dirty boxing, switching between head and body shots, and knees and elbows if we're MMA sparring. I find this kind of sparring very effective, as it causes guys that are typically outside strikers to get in the range that they're not comfortable with.
King of the Corner:
Similar to King of the Square, but you're using a corner of the gym. There's a set area of the walls that you have to stay within. The goal is to force your opponent out of the "square", to the opposite side of the corner. It's very difficult, as if you want to "win" the drill, you have to put your back to the wall and fight out of it. It goes against all intuition.
Both of these methods can be done with Boxing, Kickboxing, and MMA sparring. Rather then spend money and space on this specialty tool, use what you have. Squares and corners! Also prepare to get your liver crushed.