The K just means that it was made in Scotland.
The 201 is a great machine, very quiet and strong. Some people prefer FMQ on the 201 to the 15.
I would rather use one of the 15's. They have much bigger bobbins and you can change the bobbin even with a quilt in the machine.
The topside access to the bobbin case on the 201 means that you have to remove the quilt to get to it. And you have to do it a lot more frequently than with the 15, because the bobbin only holds about 1/2 - 2/3 the amount of thread as the class 15 bobbin. :)