Having used Q5+AM3B headphone amp module (more power) for close to one year and here's my honest thought:
1. Fiio Q5 is among the best sounding PORTABLE PLAYERS I've tried;
2. I've done several blind AB test for myself (done by a mate) and on other people who were interested in my Q5. It was usually impossible to identify which player was used when same file is being played and volume is finely adjusted to match, this includes A&K players and some other players in the $300~800$ range. And these indifferences tells a lot because I was comparing DAC+amp;
3. The only noticeably better PORTABLE player (among those I tried) to me turned out to be Chord Hugo 2. It was more revealing. I don't have the equipment to run the measurement but the difference is best described as "clearer". NOT ALWAYS BETTER but when tried with DSD/Hi-Res files playing complex Symphonies with ENORMOUS dynamics this difference is audible. Q5 plays slightly "messy" compared to Hugo2 however:
3.1. I've only tried once which took about 15mins;
3.2. No one could help me to carry out a blind test;
3.3. I'm not a Chord fan and don't usually give any shXt to the price tag so I would say I wasn't expecting any difference, but there were;
3.4. It's arguable if Hugo 2 is a "Portable" device;
3.5. The price is there.
4. I've never tried the Mojo. I was trying Hugo 2 because I wanted a new desktop DAC+Headphone Amp. I ended up with RME.
5. Connectivity on Q5 was EXTREMELY WELL. Bluetooth is connected with iPhone and never ever dropping. However one of my friend's android phone had connection issue with Q5 (dropping off frequently).
6. The USB cables included is the biggest bonus. It allows you to connect your iphone to it (a dedicated lightning to microusb cable) or some of the android phones (a dedicated microusb to microusb cable). For other portable amps sometimes you need a dedicated adapter cable to convert the plug (such as lightning to usb-A, then USB-A to MicroUsb. In Q5's boxes two cables are already included and the quality is quite good.) I bought another USB-C to microusb cable from Fiio so I could use it with my macbook (cost $20). Q5 also comes with SPDIF optical input and Coaxial input but I do think those are useless on portable players. The robust USB connectivity (tried with macbook, windows, raspberry pi sys including Volumio and Moode) and Bluetooth input are both working extremely well.
7. When connecting its line-out to an preamp in a speakers system the output voltage is lower than desktop devices. definetely not 2V, more like 1.5V or 1V. This is a bit annoying since everytime I'm testing people's speaker system they always gave a "see I knew these portable stuff are crap" simply because the volume is lower with Q5's DAC out. The SQ is good as far as I can tell but it's relatively difficult to do any blind test between like a 1V output and a 2V output, since not only the volume needs to be adjusted when switching, different volume on the amp might also introduce different level of noises which might makes the test invalid.
8. Battery consumption is quite low. I never really have it ran out of battery and I only recharge it occasionally.
9. I wouldn't upgrade to Q5S. Actually I won't upgrade to any other portable players at the moment since I don't think the SQ can go much better on portable devices. I might consider upgrading to it in future if:
9.1. DAC output is 2V;
9.2. Got Coaxial and optical output (Q5S is equipped with these I think)
9.3. Adds built-in good quality EQ.
