I've been using the 5K for about 1 week now together with a pair of Fidelio X3, for the price it's a really incredible little device, I highly recommend it.
The company also seems really passionate and down to earth, you can't say that about every company out there.
Some quick pro's and a few cons
Pros +
Price:
It just costed me around 109 EUR from their polish distributor
Sound quality:
Not much to say here, other then that my headphones sounds absoluty incredible whilst using this device, both via USB and LDAC.
Build quality:
The clip feels really sturdy, the rest of device is also top notch
Bluetooth connection:
Because of the plastic build, the Bluetooth connection is really solid.
The app:
there's so many options for various settings, many of them are beyond my knowledge, but great if you're really into the audiophile hobby
Multipoint:
The multipoint function is also great, you can choose which device to prioritise
USB-dac function
I love the fact that the device can power itself from the usb connection when it's plugged into a PC as a USB-dac, means that the battery will last longer
Amp power:
It's quite incredible that I can drive a pair of open back headphones from this tiny device, and I'm not even using it at max volume nor the most powerful amp setting
Battery Life:
The battery life is quite phenomenal, even when paring it with a pair of open-back headphones using the 2.5mm outlet I'm getting a pretty decent battery life.
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Cons -
Buttons:
I'm not a huge fan of the buttons and their placement, the actual buttons are very tactile, but both the buttons are placed in a symmetrical fashion. So it's really hard to learn which button is which unless you're actually looking at them (for the LED-light). I'd prefer a different button layout, were you can feel what you're doing with your finger.
App navigation:
Sometimes you just feel that it's a bit too complicated to navigate through the app, there's just so many options and different tabs. I'd suggest an option for a "normal mode" and a "advanced mode". The normal mode would make the app a bit more simple and more easy to navigate, whilst the advanced mode would give you all the options and settings.
Bascially I just want more information and "essential" settings to fit into the first start screen.
Another idea is being able to navigate the different tabs with swipes, top part of the screen could navigate you thorough the top tabs and the bottom part the bottom tabs.
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In total it's a clear 5/5
I'll definitely buy more products from this company in the future.
For 5k V2 I hope we'll get:
Scroll wheel for precise volume control
Wireless charging
A slightly bigger battery