There is definitely a learning curve to operating the RO 90, as mentioned above, mostly because of the weight imbalance. If you put the hose either over your shoulder, use with an overhead arm, or use one of the belt clips that Toolnut sells www.festoolproducts.com/Innotwins-Slide-Kick-Hose-Cable-Hook-s, it will help, along with the two handed technique.
After you use it a while you will get the feel of the balance and be able to work it one handed. I just finished sanding my wife's two seat, with side table between, Adirondack settee, PITA. I used every sander I own to rework this beast Ro 90, ETS & RO125, LS130, Fein Multimaster (I cut two edges off the triangle pad to get at the narrow slats at the seat, had to one hand this so the other hand could hold the vac hose), and the stick fix sanding block. I also use lots of interface pads and Festools foam backed sanding pads (www.festoolproducts.com/SearchResults.asp?SEARCH=sanding+roll), while these seem to be expensive, they last a long, long time and really cheap by the piece compared to buying Norton or 3M pads. Most important, of all this job required vast quantities of Sam Adams to dull the tedium and time involved.