Harley Benton CM-1000

Could be better but it's great for the price.
Cons (1): If the cable isn't completely still it can pick up a lot of motion noise if your trying to use this piezo in multiple ways, not only for tuning.
Cons (2): The clip-on mechanism could be a little more flexible or open a little more, but it will serve most use cases.
Pros (1): Decent quality.
Pros (2): Great price.

Cheap and cheerful. Not amazing but certainly does the job.

This cheap piezo pickup is really nice and is working well.
But I was surprise to have a jack and not a mini-jack.
The cable length is about 1m (so not long) and can only be connected to a food pedal.
I wanted this piezo pickup to be used with my favorite phone app and then have to have a big adaptator and extra costs for this use.
This would be five stars if it has a mini-jack with jack adaptator.

A good help for tuning, even though it's not top quality. It has some flaws, especially tuning low notes, but it does the job ok, and for its price it's a good accessory.