Welcome to Trulia.
I have put a lot of resources in the last 6 years to develop and maintain a network that brings me over 100 local leads per month. Trulia is an integral part of my lead generation network. I never contemplated using one of those companies as a viable business option.
You may be able to find top producing Agents who are using one of those companies as their source of business generation. I do not know any personally.
I tried them for a few months and had a bad expereince with them. Many leads were not phone verified as claimed. In addition they dumped the entire month's allocation of leads the morning of the first day of the month. The leads were not current and had been accumulating in their system. When I wanted replacements they refused and would only replace the leads that I confirmed were bad, but they never even did that. Save your money and don't use them.