The K1 is a comparatively inexpensive, portable flash-drive-sized amp~DAC which can be connected to anything with the right sort of socket or adaptor. I assume that it was aimed at people with cheap Chinese gear who wanted better sound, but that was then and this is now.
Now my Huawei Honour 9 churns out decent sound without any desperate need for an external amp~DAC like the K1. Ditto anything else I can connect this to.
The good: very portable. The shrug: dated, not necessarily obsolete, but unlikely to offer much to current devices.