I've tested this tiny mike (matchbox size) on my Ukulele (the purpose of the purchase) but also on my accordeon, classical guitar and resonator guitar. It responded well to my wishes. The sound is loud and clear.
Only two things must be said:
The mike works on a 3v tiny battery (you don't need "phantom") but there is no way to know if it's worn off. You'll need a screwdriver to change the battery (remember that if you take it on stage).
The succion cup needs to be well humidified to stick properly. Besides, the mike is so small that the succion is endangered by the weight of the plugged cable itself. You need to secure the 6,35 cable also otherwise it will pull the mike off the instrument.
It's ok if you play sitted but rather uncomfortable when you jump and dance on stage (as I do).