Just reviving this thread to add some additional praise for the RS2. I actually got mine secondhand through the FOG, but the sander looked barely used when I pulled it out of the systainer. When I first started using it, I had a lot of control issues with the sander skipping around. It was so frustrating in fact that I put the sander back in the systainer and didn't touch it again for a few months, preferring to stick with the ETS-EC 150/5.
But in the past year, I've been using the sander more and more, particularly because I've done a number of table projects that required keeping the tops as level as possible. I've finally gotten a handle on the control issues -- found a sweet spot combination of speed setting at 5 and suction at 3/4 full power that helps the sander glide over the material. It might just be my imagination, but I also swear that that the sander has gotten smoother on its own regardless of the speed adjustments. People used to talk about a "break-in" period for the Rotex, to the point where there's actually a thread on the FOG about running the sander for three hours suspended in the air to get through the break-in period. I have no idea if that's true for the Rotex (mine worked fine out of the box), but if you told me the same applied to the RS2, I would totally believe you, as the difference from my first use of the tool to now is night and day.
At first glance there doesn't seem to be a difference between surfaces done with the RS2 vs. an RO150 or ETS (EC) 150 -- they both feel smooth to the touch and look even when looking at them overhead. But bring your eye to the level of the sanded surface and look down the edge, and you will be able to see just how much of a difference the RS2 makes. Even when you're careful, a large flat surface done with a circular ROS will have dishing at various points down the edge. When you work with an RS2, though, that edge line is completely straight. It does take more patience working with the RS2 -- the first grit you use can take a long time to establish the flat surface, and it requires some self-control not to dig or press after sanding over and over on a dished spot trying to achieve flatness. But once that first grit is done, the rest of them go much more quickly. Not as quickly certainly as with an ETS-EC 150, but when you need to ace a large flat surface, the RS2 is the boss.