Exterior
I firstly want to say that I think the material choice of the QP1R is seriously top-notch. Gorilla Glass on the front and back panels, capacitive touch buttons on the front panel, solid aluminium base chassis, metal power button, metal potentiometer, and metal scroll wheel with milled grooves for aesthetics. I mean, these kinds of materials and the quality of their finishes are pretty much found in top-of-the line smartphones these days, so I think the QP1R deserves a 5/5 on that alone. You even get the choice of gray/silver or gold/copper color schemes to choose from. Not very many smartphones, let alone media players, have an option to choose a color.
However, I do have some problems with the design choice of the QP1R. For one, I don't know if it's this particular unit, but the volume knob has a large amount of wiggle room between each click, so it feels inefficient in terms of how much you have to rotate the knob in order to facilitate a response.
The other major problem I have with the design is the inconsistency of the scroll wheel rotation. Sometimes it seems to get stuck, sometimes it works smoothly; sometimes I can feel the clicks while rotating the wheel, other times I don't. It's kind of a weird experience.
Less importantly, the microSD card is so recessed into the QP1R that you need a fairly long fingernail (which I don't have) to push it in.
Also, although it doesn't affect me any my usage personally, the recessed microUSB port might be too recessed for some larger USB cables, and likewise for the 3.5 mm line-out/optical output port.
Interior
As for the internals of the QP1R, Questyle has packed some nice stuff in there. Hand-picked and tested components for the best performance, a generously large 3300 mAh battery (which is larger than a lot of modern smartphones mind you), Cirrus Logic DAC chip that supports 24/192 PCM and true 1-bit DSD decoding up to DSD128, 3X Clocks to ensure accurate timing and reduced jitter of 44.1 kHz and 48 kHz sampling rate multiples, and their proprietary, discrete, Class A-biased Current Mode Amplification technology.
The inclusion of a vibration motor for haptic feedback is also a unique feature of the QP1R that I haven't personally felt in any other media player. It's out of this world cool! When you press one of the four capacitive buttons on the front panel, the whole unit produces a pretty strong vibration to let you know you've pressed it. Heck, the vibration is stronger than my smartphone when I have vibration-typing enabled.
All of this combined makes the QP1R feel quite heavy in your hand: DSLR telephoto lens heavy. Because of this, I would recommend getting a case for one of these just for added protection in the event you accidentally drop it.
USB DAC
A thing that I often see get overlooked is the ability for a portable media player to be used as a USB DAC. With the QP1R sounding as good as it does (see Audio Quality section below), the QP1R as a USB DAC has a big advantage over other systems I have: it's so dang small while being versatile for supported sampling rates.
What's interesting about the QP1R as a USB DAC is that it can tell the computer to stream a DSD signal directly to it, regardless of the operating system. I use OS X as my primary operating system, but when I had DSD bit-streaming enabled, the QP1R's screen was displaying 11289.6 kHz/1-bit. Usually DSD signals are sent through OS X as a PCM-disguised signal, and playback of DSD128 would hence require a DAC that can decode 352.8 kHz signals (2 channels * 16 bit * 352.8 kHz = 11,289.6 kbps == 2 channels * 1 bit * 44.1 kHz * 128).
