I've got the ulra pure K and K mini with the preamp at the moment. If I wanted to put just the K and K pure western mini in my next guitar would there be less volume/output? I find the preamp a bit clunky and cumbersome in my guitar at the moment. Anyone got both?

Yes.

But it is stronger than most non-preamped signals, and sounds very good straight in.

I love the sound of the preamp but  wondered how it compares without it. Thanks for that!

Try it without and if you need the preamp get the Pure.  I just plug it in on the floor with a Boss TU2 tuner - works great.

http://www.kksound.com/purepreamp.html