Ok, I managed to install supersu installing the beta 2.52 from the iRoot recovery. I'm scared to go further.. Haha! Any news on installing other recoveries or the cm from the iRoot twrp?
Try this:
Download UPDATE-SuperSU-v2.46.zip and store in internal storage. Put device in bootloader mode. Boot into TWRP by launching command "fastboot -i <DeviceID> boot <TWRPImage>.img". (DON'T FLASH IT!)
Install UPDATE-SuperSU-v2.46.zip fron TWRP.
Reboot. Done.
Yes, if you have twrp or any other custom recovery installed on your phone, you can flash SuperSU from it, making your phone rooted. That's not a dangerous process anyway. Here's the 2.49 version: BETA-SuperSU-v2.49.zip
Following my instructions you don't install TWRP. You only boot it from a temporary download with the fastboot command.
You'll have to do this every time you want to use TWRP.