That is the insert that comes with the newest (REQ) ETS 125 (pro5), RTS 400 and DTS 400. It's universal and the slots on the right side are intended for sandpaper.
The ETS and RTS don't come in a sys I anymore. They all come in a SYS 2.
The top insert comes with all three sanders. The SYS3 I had lying around.
I've added the other two foam blocks since those photos. The two upright sanders
bang into each other without them. Finally, the DTS only fits like that without the edge guard on it.
Sidenote: Dear Festool, I didn't buy your Centrotec set because I bought the T18
after you moved it from a size one to a size 2 systainer. I put an attic lid on it,
and filled it and the rest of the wasted space inside of the systainer with centrotec stuffs and a gallon of insert bits. I carry around an Eric Cartman weight systainer for
a 3lb drill. Bonkers, I say.