Flashed Chainfire's modified boot.img, still no root?

I searched, but didn't want to hijack a thread...

I just flashed marshmallow from the factory images (full wipe) with TWRP and chainfire's boot.img (http://forum.xda-developers.com/apps...ellow-t3219344). Then I downloaded Chainfire's SuperSU 2.52 beta, and flashed it via TWRP. SuperSU is now installed but it doesn't look like root is working, even though SuperSU "grants" apps root access.

What did I do wrong?

Thanks