Product review (4 stars): Don't rely on Nesco's magnet...
The cooktop seems to work fine, but don't assume the Nesco magnet included with the cooktop is a foolproof way to test cookware.  I have a set of tri-ply stainless steel cookware that the thin Nesco magnet will stick to, but that cookware doesn't work with the cooktop.  When I called Nesco to ask about it, the company rep confirmed that with some cookware the magnet will stick but there isn't enough iron to work with the cooktop.  At the same time, she continued, there is also some cookware where the magnet won't stick but there is enough iron for the cooktop to work.

Although it's probably not foolproof, either, I suggest ignoring the Nesco magnet and using your own.  When I used a heavier magnet the results seemed to be more reliable.

One final and minor observation: the box advertises that the cooktop is "Ideal for kitchens,...and outdoors," but the sixth "Important Safeguard" in the owner's manual states: "Do not use outdoors."  I guess their marketing people and their lawyers don't talk to each other.