I also haven't heard of DDA.
I'm trying out Scout's "free" 2 searches, but it appears to be junk. According to their page, they haven't reapplied their search in 41 minutes now. I have to assume that either A. they've set up their bot to screw over the freebie option, in which case why offer it at all...? or B. Their bot sucks and only checks hourly or similar. Based on some others' comments on here, I'm guessing option A is more likely. It makes me even more resistant to paying them anything at all. Don't offer free without being honest about the situation. Geez.
I'd rather pay real humans than a bot, too. Definitely hoping to hear about DDA.