He'll probably go undrafted. I find him intriguing in the sense that his biggest problem might be partially fixable- that being his very weak arm. I quickly noticed that he is clueless about stepping into throws. One of the reasons why Colin Kaepernick has such incredible zip on his passes is because he is a former pitcher. Arm strength is a bit of a myth (sort of). Arm strength of course matters, but a good thrower knows how to put his mid section and lower body into the throw. In baseball, most of the power from a pitch generates from the lower body. It's not nearly that extreme in football, but if you aren't using your lower body right, it's going to have a big impact on how much zip you generate.
That said, if we are going to draft a QB with the hopes of justifying a trade or release of Matt Flynn, it really can't be a project type. I'm sold on Matt Scott and maybe EJ Manual (if you give him the Kaepernick treatment). As Kaepernick and Mariota of Oregon have shown, you can partially compensate for indecisive decision making if you have a cannon arm, but Klein will never have that.
I'd be fine with getting him in UDFA and putting him on the PS, but that's about as far as I'd commit right now.