It works great for its purpose. The only complaint is that the fabric used to support the panel evaporated in about a week due to the heat, as if it had turned into a fluffy substance. I had mine on the windshield.
Pros
REVERSE BLOCKING DIODE: BigBlue 10W/18V solar panel charging with blocking diode prevents stored battery energy from escaping through the charger when it is not providing power at night. With its portable size (13.19 x 9.29 x 0.2 inch) and SAE connector, it is suitable for vehicles designed for outdoor work, travel or camping.