If you do opt for a pickup, watch the HMS comparison test of the pickup models they offer:
https://vimeo.com/63940107
Based on this video, I went with MiSi Uke Trios, though it was a near coin toss with the Pono passive pickup (since I was buying a Pono tenor and bari). I did not like the sound of the K&Ks—not natural enough, and they catch too much picking noise.
I prefer to have a minimum of electronics installed, since modern electronics are notoriously designed to fail in some manner soon after the warranty expires. I also don't like cheap plastic bits (like battery compartments and extraneous controls) showing prominently on the body, nor do I like long cables snaking about the interior, visible through the soundhole and possibly rattling as you play (I have this trouble with one uke). The tone and volume controls properly belong on your amp or DI box; the ones on any built-in system mostly contribute to bad sound. And it's easier to replace, fix or upgrade the pre-amp electronics if the pre-amp is external to the instrument (or unnecessary).
That said, I think the MiSi system is reliable and fine enough that I don't anticipate problems with it, and there are no external controls and only one short cable—the only external evidence of a pickup is the jack, which serves double duty as a strap button, and so is inconspicuous when there's no cable plugged into it. There's also very little extra weight added to the instrument, and it uses a rechargeable capacitor to drive the active pickup instead of batteries (which could leak)—it takes only a minute to charge the pre-amp, and a charge is supposedly good for seven hours of use. I believe the MiSi system uses an L.R. Baggs pickup. Although folks say the L.R. Baggs 5.0 system is better than MiSi, providing the most natural sound, it didn't strike me at all that way in the video—and it's got more junk to it.