Planet13 - 5:56 pm on May 31, 2011 (gmt 0)
what can be the negative factors of using this tool, if any?
Well, you could get slapped with an over optimization penalty (OOP) and be banished to the nether regions of the google SERPs for months on end (a lot of people have reported three month penalties, but some have reported penalties up to 18 month long).
I haven't heard anything good or bad about it, so I can't say for sure. But with any link building campaign, you want the links to look natural.
also, I see that they charge monthly, but that they will post your links over time... so I don't know how much bang for your buck you get...