I use a Fishman AG (passive undersaddle) on my Gstring tenor, and I've used a Shadow SH2000 (sticky mount w/volume+tone controls) on my Flea and Fluke.
I like the SH2000 sound just fine, but I learned that I tend to smack the soundboard quite a bit and the SH2000 picked it up as a pretty heavy thump. Others played it without the thump, so I'm sure it's just the way I play. Easy to use and has volume and tone dials that are pretty effective.
I installed the undersaddle in my tenor, and I like that much better. Install was a pretty easy thing with the help of a couple YouTube how-to videos. No onboard preamp, and I prefer it that way -- I'd rather have passive pickups and use an external box to dial it in. I don't like the weight or the hole I'd have to punch in my uke for the pickups with battery/eq panels and the like.