We created this service for ourselves, used it for years, and thought it would be great to offer it to other traders. We considered a free/advertising model. However, in order to keep our database intensive service at peak performance, it's best to know who is actually using our service so we can optimize the databases accordingly. A simple subscription model gives us a definitive guide.
Currently the price is $19.95/month for unlimited broker accounts (i.e. unlimited usage).