+1 on what Alex said, and ,who has me beat by 1 sander since I only own 10 of them. Don't own any of the 5"/125mm models, and only 1 ETS 150.
Your usage will dictate what you find you need in the future. The LS130 is a nice model, but unless you are doing lots of handrails, mouldings or edge treatments, it may not be for you.
A smaller sander to compliment what you already own would be the RTS or DTS 400 models. Very nice for corners and tight, right angle spaces that you found you didn't want to use the Delta pad of your RO90 for.
Although the RTS 400 can share abrasives with the LS130, I prefer the DTS 400 over it for many tasks.