here are a few thoughts. As always what works best for you depends on how you intend to use it. I have not used a K&K pickup.
I'm curious why the K&Ks vs. the Taylor ES Go pickup? es go is a passive system. these are designed to be be installed by end users instead of a tech.
Looking at the K&K, the pure and pure+vol are both passive systems. between the 2 of them, there are other options to add volume control - something like the V-cable that has a volume control on the cable or you can control volume downstream (at the amp, using a preamp, etc). the V-cable works well (although I bump it occasionally when sitting and holding the guitar in a classical style). the pure+vol does offer a more elegant volume control as it is hidden and always in the guitar.
the Ultra is an active system. it does have eq controls for shaping the sound. Again some of this can be accomplished downstream using preamps, amps, etc if needed, but the Ultra allows you to do it directly on the guitar.
