I never used them. They seem that are quite while out there, but I checked mindstechno.com, as recommended in the reply, and I would probably use free tools to get that many backlinks with no such an effort.
i think its better to get links from people here who have reviews and share proof of results a lot of people burn though money to find a working service
Google does not like spam. Google does not like sites that sell PR. But they recognise and feed off targeted back links from well run sites where web masters charge to review a site before approving a link. There is a difference. And this you need to understand if you want to see your site climbing through the rankings.