I really like that this tool is able help me get an idea as my business grows about how many emails i'm sending out now vs what it should be at some point down road if we had more people working for us! The only thing would probably make sense to add into their service or something similar are better filters so they can narrow things further once its set up correctly (like not all users will receive every single list).
But other than those two little issues - amazing product!! We've been using them since late summer/early fall last year with great results from getting our contact lists right away which helped increase sales by over 30%.