I have not used it but I did find a couple of "rip off reports" on it.
http://www.ripoffreport.com/reports/0/306/RipOff0306827.htm
http://www.ripoffreport.com/reports/0/312/RipOff0312049.htm
Similarly, I found a post on a Yahoo message board reporting it as a scam.
http://messages.finance.yahoo.com/Stocks_(A_to_Z)/Stocks_U/threadview?m=tm&bn=73194&tid=100&mid=100&tof=15&frt=2
I also found a number of positive e-zine "reviews" of the software. Unfortunately they all were written by the same person. If he had just wanted to share his opinion one would have been enough. The very fact that he has written so many reviews makes me think he has a financial interest in the company. (Of course, I have no proof.) You can find his reviews in the list of his articles at
http://ezinearticles.com/?expert=Wally_Ashbaugh
I tend to believe the review at
http://www.startupaide.com/Marl-Doubling-Stocks-Scam.html
is more accurate and realistic.