As others have noted, the free draw tool in SpeedGrader is requires many unnecessary clicks/taps - but it would take quite a redesign to do away with those problems. But here's an improvement to free draw annotation that should require only a very minor programming change: make it actually draw where the tip of the pen is!
With all but the thickest of the pen settings, the line produced is well below the tip of the pen. With the thickest setting, the top of the line just touches the pen. With the narrower pen settings it's maddeningly hard to put a horizontal stroke (example: supplying a missing negative sign in a math problem) where you want it.
So could the pen be made to at least *touch* the line it's producing at all thicknesses, rather than drawing at a distance?