I would buy new. I bought an early production model and some LEDs went out on the pots. Kemper has been great with the customer service so no complaints, but maybe the first batch of LEDs have issues. Otherwise, I think you will enjoy the KPA.
I was one of the early adapters here in the states. My unit is still working like a champ. With used there is always the downside in certain things but also good if you can save enough money to make it worth any potential unknowns that come with used gear.
Another early Kemper owner here and I've had absolutely no problems with my unit. I also own an 11 Rack and its been rock solid as well. That being said, I generally buy new when it comes to these kind of purchases. When it comes to guitars, cars, and most everything else except shoes and clothes, I primarily look for the used item first.