You can get a free sample of progel by going to www.tryprogel.com That link you posted above doesn't work. But I ordered mine from the tryprogel.com site and I think it's the progel professional teeth whitener official website. They sent me a sample of pro gel when I oreded it anyway.

I did a little research and found this site about ProGel Teeth Whitener. Thought it might be of some help. They say that ProGel has the same strength as professional systems. I have not used it so I don't know if that's true but hope it helps.