If you are new to 3D and/or DAZ Studio, I would not purchase products that say "not tested in DAZ Studio".

As others have commented, many of these products will work in DAZ Studio or will work but the materials need adjusting for good results in DAZ Studio. Figuring out if a product will work in DAZ Studio is not something for beginners. Adjusting materials to work in DAZ Studio is not something for beginners. 

I would concentrate on learning 3D and DAZ Studio using content that designed to supports DAZ Studio. After you are more familar with material settings (the surface panel in DAZ Studio) you can look at some products that are not tested in DAZ Studio. By the way, you need to learn how to adjust materials to get the best renders in DAZ Studio, but this is not the first thing you need to learn.