reinx.guide is a "quick" setup for its own usage. like most guide in fact. I don't blame the guide writer, but not giving choice is not nice. the guide also suppose you already made backups of clean NAND, disabled DNS, etc.
I personally prefer using hekate to boot other payloads, instead of injecting reinx (or other payloads) with a dongle/payload senders.
RCM -> Hekate payload -> menu to boot different CFW or any other payload from SD card.
instead of following 2 different guides telling you to inject (and replace) the dongle with the payload you want to launch.
It's not necessarily the way everybody should do it, it's just an available option to do it like that, and options are always good to have.
You can of course do both, and send a different payload directly from dongle, instead of hekate payload if you want or don't have it setup in hekate.ini file yet.
But using hekate is easier to pick the CFW to boot into and have both fast switchable custom firmwares version.
hekate (always the same boot menu, easy to use) : choose the CFW to boot into every time you reboot. go from ReiNX to Atomsphere quickly.
Atmosphere doesn't natively support unsigned nca & nsp & xci installing, launching, but allows usage of plugins.
there's already module patches to do what ReiNX does for atmosphere.
Do i need to make a back up of my Nand before i start on anything?
if you didn't hack your swith yet and never launched any CFW, I suggest you don't use ChoixdujourNX to update, or else you'll have a "compromised" NAND before doing the backup.
just use a FAT32 SD card and let hekate generate multiple 4GB NAND dump that you can join into a single binary file on your computer. Then, update to any firmware + exFat support so your console will be able to restore NAND from exFAT (you can't restore from FAT32).
after restoring NAND made pre-exfat support, you'll lose exFAT support again.
If you already used CFW in the past, then you don't care about backing up a clean NAND, just update with exFAT support then make your exFAT backup in one single file in hekate.