I personally do not use a smartphone. Yeah you better believe that, I have a old android 3 phone that collects dust.

I work on a big Bootstrap 4.0 project and I actually sell software that is branded "responsive" without actually testing it on mobiles myself (evil customer abuser). And I need to test it on mobiles.

Personally I prefer Android but if I were into Smartphones I would probably like to dive into alternative roms and OSes, but that not matters much here. I like cutting edge tech but at the same time when it comes to testing I should probably get a android 4/5 phone on purpose rather then a android 7 right? Can I install/test multiple web rendering engines on them?

I like the Fairphone 2 for the ethical and the repair parts, but the hardware is darted but that could also be a good thing for testing right?

Also I guess I need a Iphone as well.

I looked into web based testing, seems many of this services provide testing on real devices now. Can something like this replace a real device? My guess is not because having it on your hand is something else. This services seem very expensive too.