I recently bought this device, using it as desktop amp since I had horrible sound using audio out on desktop I inherited at work. I was looking at some other options but they were all too expensive for me - I'm not an audiofile, just wanted clear sound on my new Bose QC25, not static and hiss I was getting. On Windows 10, it works pretty good, except with Groove (inbuilt music player). With it, it does work, but it stops if you press "minimuze". If you just click on another screen thus minimizing Groove - it works fine. No idea how to solve this except using different player, so I ended up using my Chrome with Google Play Music, and it's a joy. Having real knob instead of digital slider or buttons is very pleasant.
I've tried E18 in my car with Nexus 6 (improves the sound), and with intended N6, E18, QC25 combo - and that's the only scenario I don't find E18 necessary. Modern flagship with decent headphones give everything I need from them, yes It's louder with portable amp, but being not loud enough is rarely issue with active noise cancelation headphones used with phone. Ok, there are headphones that can't be driven by phone only, but QC25 are not one of those.
In short, I'm quite satisfied with my purchase. I'll be looking for some better desktop speakers now, one I use now are cheap POS,so it's quite a downgrade once I get my headphones off (I split "out" of E18 between HP and speakers, no apparent loss even with cheap splitter) and hear the same song continue on speakers.
Fiio did a great job here, creating useful, multipractical device that sound good, looks and feels awesome and has multiple use scenarios and load of manual controls, compared to products in same price class. I'd highly recommend Kundun.