I figured that someone would have responded by now...
I have not personally had any experience with this company, but I have the impression that there are questions about them. You should do a Google search and see what you can find out. There was even a posting earlier here on beatthegmat concerning this company. You will see that posting on the Google search.
I will say that often you get what you pay for and so many questions for $15 seems a little too good to be true!
Have you tried all of the official materials = 11th and 12th editions, 1st and 2nd verbal and quant, the sets of GMAT paper tests, the Quant focus?
If you have and still need more questions, there are lots of posts on the forums reviewing various books, practice tests, etc.
Good Luck!
