I once had an Ohana Vita with that Mahalo pickup installed by a guitar shop guy:
The pickup somewhat works reasonably well for something I paid around $30 for.
But it did have some issues to do with some hissing at high volume, the middle strings sounding louder than the outer strings and the wires rattling in the body while playing.
The string balance was fixed up by the guy who set it up (though I think the G string was still a bit weaker than the rest), and it "worked" as a pickup. But having tried better pickups, like the Shadow Nanoflex on my Kala, it is clearly inferior. The money you save may not be worth it in the long term.
The dilemma with the better quality-pickups is that they sometimes cost just as much (or more) as a good, inexpensive uke that comes with that same pickup factory-installed.
To put things into perspective:
The Shadow Nanoflex pickup by itself for Ukuleles costs a whopping $199.99 AUD if you order through an Australian music store.
A brand new Kala KA-CE Mahogany Concert from MGM costs about $200 AUD including shipping, complete with Aquila strings, hardcase, other extras with the same Shadow pickup built in.
A Legacy laminate spruce-top Soprano with the Shadow pickup built in just costs $179 AUD ordered through a music store's catalogue (they're pretty nice).
And well for a $400 Fishman pickup mentioned earlier, you can buy a very good uke with a very good pickup >_<