I read before bed but am unsure if I should be using a no back light Kindle or if the Kindle app on my iPhone is ok? Anyone have experience with sleeping quality after reading using either of these?

For me, yes. I notice that whenever I'm reading on my phone (night mode, blue light filter, lowest light setting), I will stay awake longer, my eyes strain, it takes me longer to fall asleep. When using my kobo (not backlit, but still lit - it has those leds all around the screen that light it up from above!!), it's like I was reading a paper book, except I can read in a dark room without any strain to my eyes whatsoever, and I can take on any position without having to adjust the light source!!! An absolute game-changer in terms of comfort. In fact, I think my eye strain is even lower with the e-ink reader compared to regular paper indoors, because I have a better light source no matter where I sit in my room.