I was a little skeptical about whether the Speed-Micro Actuator version was worth it but after receiving the cube and doing a couple dozen solves I must say I'm impressed with the performance of this cube. It feels much like other MGC cubes but has a much smoother glide on the outside edges and it's slightly better on the inside. It seems to catch a little bit less than my other MGC cubes and I'd also say it's a little bit louder due to the bearings. The setup was great out of the box but I may let the tension off a bit to bring it a little more in line with my other MGC cubes.
The SMA mostly effects the outer layer which makes the 3x3 part of the solve feel a lot more like a speed cube. It does feel like it speeds up the second layer a tiny bit but not nearly as much as the outer layer. On the 4x4 it's nice since all layers are beside a SMA but I doubt this slight speed gain to the second layer would translate to the third or deeper layer on larger cubes. That being said I wouldn't hesitate to purchase the SMA 5x5 when it releases.
Though still difficult this is the first cube larger than a 3x3 I've been able to successfully hit a 270° M-slice when doing algs such as U-perm which helps bring it more in line with how I'd solve a normal 3x3, especially using algs that only require a M2 which I can consistently hit with relative ease. It's also the first cube I've been able to perform a single action 2R2 when doing parity although the 2R2 is still quite difficult for me to nail consistently. I tend to undershoot it by about 20-30°.