I’ve never used the Mirka CEROS but I do have the ETS 150/3 and ETS 125. For the ETS 150/3 I have a wide selection of Festool Rubin, Brilliant-2, Titan and Platin abrasives. For the ETS 125 I have Festool Brilliant-2 and Mirka Abralon and Abranet abrasives. I have rubout pads for both sanders but mainly use the Rotex RO-125 for this work.
My sanding is mostly for furniture work. If I could only keep one of the two sanders for furniture work, it would be the ETS 150/3. It is the most user-friendly 6-inch sander I ever used and is totally reliable at all times at all speeds. I use it where I wouldn’t have the nerve to use any other brand’s sander over 5 inches. There has never been a time when the ETS 150/3 didn’t have enough power or wanted to slow down. It has also never gouged the work.
The ETS 125 is a completely different animal. It is my favorite sander for inlay and marquetry work. It is gentle and totally reliable when you are doing very fine work, such as sanding off veneer tape over 1/50 inch thick veneer. On solid wood projects it feels under-powered at times and wants to slow down.
As for the abrasives, in my opinion Mirka Abralon is essentially the same as Festool Platin. They are virtually interchangeable.
Mirka Abranet is unique. On narrow projects, such as sanding the edge of a board or a surface much narrower than the width of the sander, I get better dust collection with the Abranet than the Brilliant. My Abranet sheets are all 5-inch diameter, and I’ve chosen to cut them down when I need abrasives for the triangular shaped pad of the DX 93. If you choose to use Abranet, you should use the Mirka interface pad so that you don’t prematurely wear out the Festool Fast-fix hook and loop pad. Abranet is available in P600 which Brilliant-2 is not.
Hope this helps.