In the review of the RO 90 DX multi-mode sander written by Cliff the "Wood Nerd", he mentions that initially he struggled with the balance of the machine. The weight of the motor in the rear of the sander combined with the weight of the dust extraction hose were making it challenging to keep the pad flat. This brings up a very important point about how proper technique can make a noticeable difference in the performance of a tool.
In the photos below, Cliff discussed the different types of grips he used with the RO 90 DX. He began with the grip shown in the left-most photo. Your instinct may be to grab a Festool Rotex sander or the Festool Domino in this way. The issue with this technique is that you have a single grip point where you're attempting to balance the tool and keep the pad flat on the material. Likewise, on the Festool Domino joiner, you're leveraging a single point on the tool to balance it as you plunge into your material.
The technique that we recommend is shown in the center photo. Keep one hand directly over the sanding pad for controlling the movement of the sander. Use your other hand on the very rear of the sander, or even grab it by the dust extraction port and power cord. The back hand then supports the weight of the machine and helps maintain proper balance resulting in perfectly flat contact between the sanding pad and material. With the Domino joiner, you would use a similar technique, keeping one hand firmly on the handle on the fence while balancing and making the plunging action with the other hand at the very rear of the machine.
Cliff introduces a third option, which you may want to try. While it's difficult to tell in the right-most photo, he has wrapped the dust extraction hose over his shoulder. This helps offset the weight of the hose and makes it easier to use the sander with a single hand.
Keep this in mind when you're using any of your tools. The user of the tool can introduce factors into the equation that can alter the end results. Happy sanding with your new RO 90!