Since Orfox is based on a pretty outdated Firefox version by now, I'm a bit worried about its security. Is Orfox still being updated / can we expect it to be patched in the near future?
Orfox will be sunsetted by early 2019 when the stable Tor Browser for Android comes out
Orfox has stopped long ago and therefore it is not secure to access the deep or dark web with that.
Furthermore, when you want complete anonymity and untraceability better use a computer running live operating system like TAILS.
Tor Browser for Android (Alpha/Beta/Stable) is for some basic anonymity but you can be traced easily since your phone is running services that you might not want to be sending your IP through the internet while being in the depths of the web. Needless to say that you cannot "kill" these services or your phone will reboot the moment it understands that those were killed. (Thank Google for that)
There is already a updated version of Orfox called Tor Browser for Android (Alpha).