I can confirm this. The radial menu allows you to customize each application you're in. In other words, each application you open will have it's own uniquely customizable radial menu and will change depending on the currently active application. If you're in Chrome you may have a back,forward, bookmark option, etc. In word, it could be undo, redo, bold, italicize, etc.
HOWEVER, the remapping of the surface size buttons seems limited to only a GLOBAL view. Meaning that it is NOT customizable per application (yet) and will perform the same no matter where you are. The ONLY options that this will allow for is remapping the two side buttons (eraser and right click buttons) to these three options.
-right click
-middle click
-radial menu (pops up the radial menu when you hold down the button and touch the screen)
This is good for the application but very limited for any other purposes. One of the SP3's buttons already IS a right click, making this a silly choice to remap, the radial menu could be useful assuming you want to use that application. The middle click is not necessarily useful, but could have interesting functionality. For instance, if you're an Autohotkey user I think you could set up a script to do something like...
...
IF you're in (specific application)
AND you hit the "middle click" button
THEN (using autohotkey) remap middle click to keypress of your choice
ELSE
just perform normal middle click
This autohotkey concept is just speculation, and I have no need to try it out, but so long as the radial menu truly remaps it to a recognizable middle click, then there shouldn't be any reason why you couldn't remap it. Recognize, however, that you only have ONE programmable button since Autohotkey doesn't have access to the radial menu and therefore can't detect it's triggering, and while the middle click may be able to be remapped, in virtually every application you need to use the right click at some point, making it something you wouldn't want to remap.
Just sptiballing here, but yes, you can remap the two side buttons to middle click.
-Mike