Kevin, this is what Scouts Inc says about MacDonald:
Frequently lines up on the outside and can cover defenders in space. Has the potential to be an effective in-line blocker. Flashes strong punch and gets into sound position. Athletic enough to seal front side and cut off backside as a zone blocker. Gets to the second level quickly and can cover up linebackers but body control is adequate and can whiff in space however.
I don't see anyone dropping more balls than Walker. He caught 21 and dropped 9. That was the worst rate in the league. MacDonald doesn't have the speed to create mismatches, but he's going to see the field. I have a feeling, though, that if Manningham is healthy or if Jenkins develops we'll see more 3-wide sets.