Question about root and roming on OC3

So I bought an S6 that has OC3 on it and I want to root it and install clean rom on it.

Is this guide safe to follow?

http://www.phonearena.com/news/How-t...cluded_id69135

And then just install flashfire like a normal app and flash?

Is 0 a good price for mint s6+box+cases+glass protector? on a m9 now