I just wanted to add my experience with Disney Dinning Buddy.
I was looking for a reservation (California Grill) for 4 people on a specific day between 6-7:30pm. I had no interest in anything earlier or later. Dinning Buddy will search your time as well as 2 hours before and 2 hours after. So, if I put in 7pm, it searches from 5-9pm. There is NO WAY to limit the time. So, I got a text message every hour, on the hour, for an 8:50pm reservation that was available. So, I changed my desired time to 6:40pm (so that I wouldn't keep getting texts for the 8:50 reservation). Then, I kept getting text messages every hour on the hour for a 5:15pm reservation. Again, no way to adjust this. So, I kept getting text messages once an hour 24 hours a day (including the middle of the night). I even ended up booking the 5:15 one just to stop the notifications for that; but then another time opened up at 5:30 and I couldn't book both of them. So, I ended up just shutting off the notifications for this one.
The other reservation that I was searching for was arrival day Ohana dinner between 6-7:30pm. Well, from my experience with my California Grill reservation request, I knew that the site looks once an hour, on the hour, every hour. Well, I ended up searching myself whenever I thought about it and noticed that it wasn't on the hour. I ended up finding the reservation I wanted (7pm - perfect) on my own, with no help at all from DDB.
I paid for DDB to search for both of these reservations and it did not help me one bit. I have heard other people have fantastic results from the website, and those people seem to be quite happy with the service. I just wanted to offer another point of view. Best of luck with your reservations, no matter what you end up trying.