Low Down on Solar Mats??

I am thinking about buying a solar mat, but am not really sure if it's a good investment or not. I have been trying to read all the posts on them, but majority is how to fix them or have to do with flow. I would first like to know some basics. I have a 15' round 7,500 gallon AG pool. What's a good brand? I saw one in In The Swim sales catalog for like $129 for a 15 foot pool. is that a good idea? Also, what is the average heat gain by a solar mat? I know everything varies, but if someone could just give me some basic info (hints and tips) that they have learned over the years that would be great? Thanks!