If you trust it, then I say it's ok to pay the $50 to see what happens. The best thing to do is to make sure you have a Google Analytics account and track your improvement in rankings at engines from new backlinks, if backlinks is what they are offering. I wouldn't hope for traffic from something like this because traffic only comes from pay-per-click and organic engine listings.
I have not yet used that tool, but as i've gone thru few forums and seen the reviews of people about that tool...... i think the tool is fine. Just make sure it it brings a limited links per day.... coz google don't like huge backlinks in just one day.
As a rule of thumb , if you really want to have links that last longer and quality related links, please stay away from automatic bot or software that will do you more damaged that good ... i tried so many one so called set it up and forget it software those are nothing but crap ... i rather write articles submit to article directories it takes longer but i know I m getting a long lasting quality link without spending on overated software
Social bookmarking is a method for Internet users to store, organize, search, and manage bookmarks of web pages on the Internet with the help of metadata, typically in the form of tags that collectively and/or collaboratively become a folksonomy. Folksonomy is also called social tagging, "the process by which many users add metadata in the form of keywords to shared content".
For more information please refer to this link http://en.wikipedia.org/wiki/Social_bookmarking