We have been able to use the free version of benchmark which is helpful. When we have tried uploading some of our lists into similar sites, we would just be told the list was rejected. Benchmark actually walks you through some possible problems with the list might have.
I personally feel that the actual creation of emails is a little more difficult than other possible tools. Its interface is also a little less robust.
Benchmark is a great way to start sending marketing related emails. If you have a list larger than 2,000 it will no longer be a free account.
We have been able to use Benchmark to help us clean some lists and also send some successful email campaigns.