Hey Paul, I can't speak to the quality of BrightTalk leads because we did not end up going with them.
They had very high CPL & upfront costs from what I remember but the biggest reason why we didn't sign on with them is because we segment leads based on company revenue and BrightTalk segments leads based on a company's employee count. In the past, targeting leads based on their company's employee count proved to be ineffective for us so we didn't want to take that chance again.
That being said we were all delighted with the BrightTalk employees we met, they seemed to have a very active & engaged community and the overall UI was pleasant to look at. Maybe in another life...
Hope this helps!