This and That:
Comes with screen protectors (already applied and a spare one), USB DAC cable, USB charging cable, protection case made of hard plastic (silicone or pleather would have been my material of choice).
Decent design, form factor and build quality. The rear glass panel is a dust and fingerprint magnet though.
Screen resolution and viewing angle decent. Not very bright though.
Fluent and responsive navigation and operation. Touchscreen. Decent benchmark scores. No delays or whatsoever.
Two gain settings and 100 system-wide volume steps. Listening very quietly is fortunately possible.
Supports in-line remote control commands (at least play/pause; volume adjustment doesn't seem to work).
Based on Android 5. Thankfully comes with Google Play Store.
Hidizs-customised Hiby music player. Intuitive, modern interface. Nice folder browser. On-screen keyboard search feature. No track counter on the playback screen, though.
Internal memory plus micro SD card.
Unfortunately some occasional WiFi interference noise through the headphone if some other WiFi sources are nearby. It's acceptable for a desktop DAC that's not designed with internal WiFi streaming (such as my RME ADI-2 DAC), but a shame for a dedicated streaming player (funny how mobile phone manufacturers get it right; my Apple iPhone 4 (with Jailbreak and added finer volume control) is still one of the best audio devices with decent measurements for wireless music streaming).
Gapless playback works as perfectly as it should using FLAC files.
Battery Life:
Playing FLAC files as well as occasional WiFi streaming with the volume set to 50 out of 100 (low gain) with the Superlux HD668B as load and with occasional unlocking and navigation through the menus lead to 8 hours and 30 minutes of battery life.
Sound:
Frequency Response (no Load, Digital Filter #1):
No surprise; just as flat as it should be.
Frequency Response (complex Load: Ultimate Ears Triple.Fi 10):
Hidizs state around 4.8 Ohms as official value. The actual calculated output impedance is however around slightly lower than 7 Ohms.
Even if the AP200 measured and performed to specs when it comes to output impedance, which it doesn't (the AP60 does neither), it would be a bad choice for loads that don't have a flat impedance response. Disappointing.
Hiss Performance:
Fortunately only quite little hiss with a very sensitive dynamic driver in-ear such as the Ostry KC06A. So ultimately not as good as my iBasso DX90, but way better than the Hidizs AP60 and better than many other devices on the market.
Subjective Sound Perception:
No surprise; it sounds just as clean, transparent and neutral as any well-designed audio device should sound. Unfortunately the high output impedance drastically limits the headphones that can be driven linearly without any frequency response deviation.
Bluetooth:
As transparent as expected thanks aptX codec. Identical sound to any other aptX transmitting source I've heard, no surprise here.
Conclusion:
Surprisingly good but the high output impedance (already high official specs, and even higher real-world output impedance) is a major turn-off.
Smartphone manufacturers do a better job at getting the WiFi interference shielding right (occasional interference noise when the AP200 is close to other WiFi devices).