This must be a joke.
In order to service the valve on the slash you must remove 13 screws, rear bottom plate, air tank, trigger plate cover, and the magazine latch.
To service the valve on the k1 only requires the removal of 2 screws, rear cover plate, and a spring. The valve is removed during the degassing process. No other airgun is capable of this feature.
Both guns use specialized tooling to service certain parts.
Quality of after sale support is dependent on country. In America we can easily get parts and great service for the K1.
As far as build quality, I give a slight nod to the Slash. The chassis looks to be more solid than the k1. The trigger linkage has a better design. Taipan had a lot of practice with Bullpup triggers so no surprise there. Both guns are amazing but to say the K1 is more difficult to service is.. false.