I went through David's DVC last year for a studio at BLT and I was happy with the service. He does charge $13 per point which is a little higher but I felt better going through a service then an individual owner.
My reservation showed up quickly on Disney's website, so you can see it and it relieves any anxiety that the service isn't legitimate.
The only thing that was a slight con was that once you decide what you want you pay in full and it's yours. You can't make changes and I'm someone who is indecisive so I felt kind of locked in.
For my vacation coming up, If I went through Disney's site I could get a BCV studio for $1580 with 35% off. The same studio through Dave's site would be $1300. In the end we decided that we wanted club level though.