I tried one of those services.. 10,000 in a month for $24.95 and found many of the visitors were from non-US, non-EU markets which visited between 1am and 4am, I'm Central US. (Very few of the IP's resolved to named addresses)
The company guaranteed 10,000 unique visits or would pro-rate a refund.. in the last 3 days of the time frame.. I got about 7,700 visitors, so I cannot say it was balanced traffic, but I did get 10,000 visitors.
Granted, it was 'untargeted', cheap traffic that I was using to test the site as well as the service..
If I may make a suggestion.. use a specific landing page (e.g. A renamed copy of your index page) or hang a variable off the URL you submit to the company so you can track performance. (
www.domain.com/index2.html?source=june_ad)
If you can, put a banner from an advertiser such as
Fastclick on the landing page to help defray the cost.. They have pay-for-impression programs.