I'm embarking on my first DIY project shortly of a tarp. I'll be borrowing my mom's thread injector (along with her for guidance) to complete the task. If it all works out well, and I decide to make some more stuff, I'd like to look into purchasing my own thread injector. Our local Kijijii has a ton of them listed, from 100+ year old machines to ones form the 70's and 80's.
I personally prefer the old metal singers for appearance, but what do I actually require from a machine as far as what it can do?