My general comments on the Rotex sanders are "you should buy one only if you really need the aggressive material removal". I have both an RO 90 and RO 150. They are excellent machines and serve the exact purpose they are meant for - aggressive fast material removal. In my case, I had about 160 feet of fencing that needed the stain and rough surface sanded down. The Rotex machines performed much faster than any other random orbit sander. However, there are compromises.
The smaller RO 90 is excellent if you absolutely need that tiny 3-1/2" sanding pad. I had to sand small insets in between fence boards and this was the ONLY tool that would too it. Another thing is that if you are doing heavy sanding, the section behind the sanding pad will clog up with sawdust and the dust collection will stop until you remove the sanding pad and clean out the small sections behind. I had to do this about every 4 foot section of fencing that I was sanding. Also, while the RO90 comes with a triangle delta head for sanding internal corners, it's extremely difficult to keep the sander even with the surface (the weight makes tilting the sander really easy).
One element that the RO 90 is excellent for is if you have smaller concave sections that need sanding. A larger 125 (5") random orbit could just be too big for some sections. I have seen the RO 90 being used to help shape/smooth areas of chair seats (which have a lot of convex/concave surfaces).
The RO 150 is a beast and will remove material really fast, but it is very heavy and loud. If you are going to be using it for longer than 1 minute, you absolutely need hearing protection. While you could potentially use it one-handed in "random orbit" mode on a flat horizontal surface, the RO 150 is really a 2-handed tool for any realistic operation. That being said, I have pulled out the RO 150 to do quick material removal on some projects (like taking down 1/4" of material on a box/cabinet that was already glued together).
I think I have seen where the ETS EC 150/3 works better/faster than the RO 150 when the RO 150 is in "random orbit" mode. The RO 150 is obviously faster when in "rotex" mode.
The Saphir 24 extreme grit paper has it's place and it's useful for doing stuff like taking off plaster (such as what Bob was doing). However, if you are trying to use it to take off paint/stain or trim down material, I found that it's not nearly as good. The 24 grit elements on the paper are so large that you essentially are grinding big scratches into your wood. A 40 grit Rubin paper actually works smoother and faster for taking off paint/stain and removing wood material. I found that the Rubin paper works slightly better on wood material than the Granite paper.
If I was in your shoes, I would probably look at an ETS 125 for finishing sanding. Your ETS EC 150/5 is excellent for material removal and stuff like sanding off excess glue, but it doesn't do as well for the fine finishing sanding. The small 2mm orbit of the ETS 125 combined with 220 grit results in an absolutely smooth surface that is excellent right before you apply finish.
But if you really want a Rotex "for the fun", don't let me stop you from buying it. It really depends on how much "fast material removal" you need. If it's infrequent, then I think the 150/5 will be just fine.
