I have a 3 different teapots and it always fascinates me how much the taste changes depending on which pot I use, given all the other variables being the same.
I also use a shimizu ken teapot, but mine is the reduction version, it's not oxidized. I'm not sure what the differences are between the two, but I use excusively sencha in this teapot. It does seem to reduce the aroma moreso than my other teapot, but I find it gives a nice roundness to the flavor. It's definitely my favorite teapot. ever.
Water and tea are of course other considerations. the clay really works best with softer water, like out of a real tetsubin. though, I would say all sencha works best with testubin. If the water you use is filtered from the tap (like me) and you don't have a tetsubin then perhaps you could experiment with different waters with your pot. Fiji water, while expensive, was always my favorite before I started using the tetsubin.... it's a bit softer taste and I found it went well with sencha in general.
as for tea, quality pot deserves quality tea. I drink japanese rokucha (sencha etc) exclusively these days so I have no real experience with this pot with other types of tea. Practically anything from the mid-range up at o-cha.com or ippodo should work well. I have to say my favorite place for tea lately is thes-du-japon.com, you can find a number of very interesting sencha and some for pretty affordable prices.
Of course if you want a real wow, may I suggest their "sencha de tenryu" which is excellent (though pricey). their "koshun" from fuji,shizuoka is also very good... and perhaps my favorite tea of all time (when it's available... probably later this spring) is their "mariko sencha, kondo wase".
for specific differences between the reduction clay and the oxidized clay, or for just general guidance with the oxydized clay as far as tea is concerned you could contact Akira Hojo, from hojo.com. Guy sold me my pot and is friendly and knowledgeable.