[One (M8) General] redpoint73:
I agree with all that Einwod said in regard to toolkits and YouTube videos. Plus, the toolkits all contain old TWRP and SuperSU files, that will cause many problems. The toolkits don't accomplish anything, that you can't just do "manually" with simple fastboot commands (as described in the guide in the top post). And frankly, if you can't do fastboot commands, you probably shouldn't be rooting the phone in the first place. But as long as you take some time to read and understand the process, and follow instructions carefully, you should be fine.

Be careful of YouTube videos. As Einwod mentioned, they are pretty much all out of date, and that will cause you problems. The other problem with following YouTube videos, is that is usually shortcuts the learning process, and shows you just enough to get into trouble. While glossing over some of the important nuances; and most importantly

how to recover

when things go wrong (and they will at some point, no matter how careful you are!).

Important points to consider:

1) Vomer's guide is mostly good (at least for unlock bootloader, custom recovery and root) except the files linked are out of date. Use current versions TWRP (right now 3.2.1.-0) and current versions SuperSU (right now 2.82) or even better Magisk (at this time 16.0). The exception would be if your M8 is on older firmware (older than Marshmallow) in which case, you should update before unlocking the bootloader.

Additionally, the s-off method (firewater) in Vomer's guide no longer works. But you don't need s-off for custom recovery, root, custom ROM. Stop once you reach beginning of Section 2 of the guide, as the remainder of the guide is not needed.

2) Backup everything. This is a big one, that many tutorials skip (at your peril). Your phone will be wiped when you unlock the bootloader. So if there is data you want to keep, copy it to your computer, cloud, SD card, etc. Once you install custom recovery TWRP, make a backup of the stock unrooted ROM before you root. Again, this is something most tutorials (especially YouTube videos) don't tell you. Not only does this give you a way to recover if something goes wrong while trying to root; but also give you a stock unrooted ROM, if you ever want to revert (for whatever reason).

---------- Post added at 11:15 AM ---------- Previous post was at 11:12 AM ----------

I don't personally use a Mac, but it should be fine. This (Vomer's) guide has Mac specific instructions. You can use any computer (PC, Mac, Linux) as long as you can get an adb/fastboot environment setup.

---------- Post added at 11:31 AM ---------- Previous post was at 11:15 AM ----------

Well, of course there is. Otherwise, why would there be some many folks developing, posting, and flashing custom ROMs? Now, what each person needs and prefers will vary greatly from one person to another. So that doesn't mean that custom ROMs are right for

you

. But some reason for custom ROMs:

- Custom Sense ROMs: with mods and customization options, as well as performance tweaks. ROMs will also have bloatware removed already. However, what one considers "bloatware" is subjective. So the degree of bloatware removal, as well as addition of other features, may or may not be to your personal liking.

- AOSP ROMs: ROMs without Sense and therefore close to a "stock" (Google) Android feel. This is a big reason for custom ROMs. Some folks simply don't like Sense. Additionally, Sense ROMs stop at Marshmallow. AOSP ROMs are available in Nougat and Oreo (although some things may be broken) and beyond, as long as their are developers willing to keep supporting this device.