Magisk: can it be used by mere mortals? I just found out about Magisk and it sounds great,  but I don't't know much about it.  How would I use it?  The phone's a ZTE Z815.
Sure it can.  It's actually pretty easy as of version 14.  You'll need to unlock your bootloader and instal TWRP.  That's the hard part.  It looks like there are ways to root it, but XDA-Developers doesn't appear to have a forum for it, and that's where to go for trusted advice and mods.

If you can get those two, then you can download the Magisk zip file, boot to TWRP, and install it.  Next, update the stub Magisk Manager application, and you're good to go.  I strongly encourage you to then instal Xposed (all systemless)