satechi

tl;dr: It's a power meter, not a protection circuit. It works well and is worth the money if you need to monitor power consumption, but it's made of plastic and doesn't feel like it can take a beating, so handle with care.

For some time, I've used a PowerJive USB Power Meter to measure the charging rate of various USB power adapters, and even things like how much power a Rasbperry Pi uses under load.