The Xone k2 has a very good built quality as you expect from Allen & Heath. It is very portable and comes with its own case. The K2 has 3 latching layers which means 3 banks that you can use for your personalized mappings. You can easily configure it's midi channel and which buttons/ knobs can be affected by the latching layers. You can connect multiple k2's with each other via Xlink or connect a k2 with an other xone mixer that has xlink, which is a big plus if you have few usb's on your laptop.
The only think that I don't like is the built in sound card due to it's driver and also it doesn't have good latency. If you have a xone 23C, 43C, DB2, DB4,PX5 this should not effect you but if you use any other mixer then I recommend to purchase an external soundcard.
Overall all I am satisfied with this controller, I recommend this controller for those persons that like to create their personal mappings. Also it suites very well with traktor or abelton.