I have a ddc account. There isn't a minimum on the number of names you submit to get an account, but there is a minimum on the quality of the names. I can attest to that because I only submitted one name and got approved.
For reference, the name I submitted is an adult name that gets 50+ type-ins per day. (not 50 uniques coming from expired traffic ect, but genuine pure type-ins almost all from the usa) I have been running the name for 1 to 2 months on each parking company and will eventually decide on where to keep it long term. I just finished testing ddc and have moved onto parked.
As for a comparison between services, I can point out a few things.
The configuration options at ddc are minimal/nonexistant. That could be seen as a bad thing, but really since they only take on premium names and they take the time to setup and optimize each domain for you, I didn't see it as a problem. I did kind of miss the ability to tweak things.
Comparing this one name between Parking Panel, Parked, Sedo, and DDC:
(everyone I've tried so far)
Parking Panel RPM was $8.34, CTR 62% (lots went un-counted...)
Parked RPM is currently $30.71, CTR 85%
DDC RPM was $32.99, CTR 45%
Sedo ???
Namedrive wouldn't monetize the name (too graphic)
I didn't get a number for sedo because I couldn't bear to leave the name there long enough to get a stable calculation. Even though sedo occasionally pays really high per click, the adult lander is so terrible that it isn't worth it. CTR at sedo was less than 20%.
Of everyone I've tried so far DDC and parked are neck and neck. DDC pays alot more per click, but seems to get less clicks. Either because the lander gets less clicks or because there is more traffic that they disqualify, I'm not sure maybe a combination of both. It is looking like parked will make just slightly less than ddc did, but with some of the parked benefits i'd judge the two to be about equal. Bi-monthy payments vs net 45 may give parked the advantage, but I suspect if I had a name that wasn't adult in nature ddc would be able to do better earnings wise than parked.
I haven't been able to qualify anywhere with a skenzo feed just yet, and I also don't quite have enough good names to get into sedo pro. (well I might, but there is no way I'm moving my best earners away from where they are now to sedo for a couple of months just so I can qualify for a sedo pro account to find out if they
might pay better.)
Overall, ddc is comparable to the best services I've tried. I wouldn't bother trying them unless you have a premium name though. I can't judge the service of their reps because I make it a habbit not to bother the rep unless the sky is falling. Not much came up during their test that gave them a chance to prove how good or bad the service was.