I understand the cons to the equation: they already drafted one this year, they have a winner in Shawn Hill, and a potential talent in Alex Smith. It's getting crowded back there and Singltary isn't exactly drooling over the Idea of running a shotgun-style passing game.
There are, however, some positives to at least entertaining the idea of bringing in Harrell.
For one, he might be great. He may surprise teams with his game time performance. running drills is one thing; making the right decisions under fire is another.
Additionally, he understands why they took Michael Crabtree in the first round. Harrell has first-hand knowledge of where Crabtree will be, why he should throw to him, and how to get it there.
Although Harrell may not be bursting with arm strength or lightning-quick open field moves, he can run an offense - especially the two-minute offense.
Is trying Harrell on for size to see if he fits a big risk? If he's signed to the league minimum, probably not. What's a little more friendly competition at quarterback in San Francisco right now anyway?