The is to have a panel pointed to the sun.

If the panel is easy to fold out or if it rotates to get the most intense sunlight or sheet panels that you can basically stick to anything sounds like a good idea but what is the trade off for these things? I have seen many of these on Ebay for very cheap but they all look like scams.

It just makes sense to put a panel pointed to the sun and thats it but does the mobility of fold out panels a good idea?