Thanks a lot for the uplifting advice. I really do appreciate that quick response. I'm curious, do you have one of those version 15 Onyxes yourself?

Probably flashing is only half as bad as it is in my imagination. But all the information I read is very confusing (for someone who certainly hasn't had much to do with the Android world apart from flashing the Nexus 5), since it's always bits and pieces, never a straight step by step process from "unboxing right through to booting into SFOS".

For example, the instructions in the link you provided state that after downloading the zip and the specific twrp, one is to "Boot into recovery, first flash the oos2.2.1-x.zip". I have no idea how to imagine that step. Is that some Onyx stock recovery? If so, where can I find a step by step guide?
At what point does one install twrp?
And will this twrp-3.0.2-0-onyx.img definitely work on the version 15 onyx?

At https://wiki.merproject.org/wiki/Ada...Pre-requisites I read about a specific OnePlus X ROM and a particular twrp one is to use, both of which seem to be different from the ones in the other post. So, I wonder how they would interact with SFOS.

In summary, this still seems like a rather large risk to me. After all, I don't want to buy and brick the phone within only a few minutes.