I'm no QB coach, but: Harfield looks to be really promising. Here's what I noticed right away. Height: at 6'7" he's obviously got no problem seeing the field. Arm: It's hard to really judge arm strength from these videos, but he looks to have a solid combination of strength to zip it in when necessary and touch to drop it in on the longer passes. Most impressed with: Pocket poise. So many young and mobile QBs panic when pressured and immediately look to run. He is mobile enough to get out of trouble at this level, but looks to find space to pass. This is a kid that gets it - he'll make more plays with his arm than his legs.
Concern: 6'7" and 191 pounds - he's going to have to beef up. Somebody might break him in half if he doesn't. That's an issue that's easily fixed, though, once he's on a college workout program and schedule.
Mayock: Again, hard to judge on the video, but he doesn't look to have blazing speed. He does seem to have a knack for getting open, though, and shows great ability to focus on the ball and come down with it in traffic. He's a kid that coaches would definitely want to see in camps - although I'm sure he's been to some already as a '15 grad.