Its a good tool for tuning. If you have those rectangular big chromatic brick tuners, buying one of these makes it way easier to tune your uke accurately. I've never used that particular brand, but I've used some really cheapy versions, and they work just as well as my more expensive ones.
And you can also clip it onto the head and plug it into an amp. But honestly, it is not reccomended. It doens't sound that good, and the signal is pretty weak, since you'll be clamping it to your headstock (i tried clipping it inside the soundhole, and it just doens't work b/c it gets in the way of your strings.
So don't try to use this as a substitute for an installed or another type of stick on pickup, but for tuning purposes, its great.