An m.2?
I considered one of those but the connector being underneath the motherboard was too much faff so I got a regular 2.5" SATA. Just realised I'm not sure if there's anything in the case to mount it though, probably need a 3.5" bracket. Arse.
So, no brackets, tape, nor dangling necessary. :)
Guess it's because Mini-ITX has limited space, and putting it next to the SATA but on the reverse is probably the most efficient layout - a quick search shows other Mini-ITX boards also have it on the back.
Had the connector been more conveniently accessible I probably would have gone for m.2, but SSD will be good enough, and (once I've got it setup) I can remove the 3.5" HDD and will have absolutely no moving parts. Hooray! :D