I looked up the video of Manziel being injured against Auburn, and the way he was hit is the same way Rodgers broke his collarbone; ie, you don't want ANY quarterback coming down like that, directly on their shoulder. That doesn't indicate to me that Manziel is 'fragile' any more so than someone like Cushing is for taking a hit that usually causes an injury. And Texian is technically correct: Manziel isn't exactly stocky but Bridgewater is a bit skinnier by comparison, though it shouldn't make a huge difference.
I'm also on the Manziel bandwagon if only because of his eyes: he sees the field better than anyone else, and has improved at making reads. It's what makes guys like Drew Brees so dangerous, though I'd argue Manziel's athleticism takes it to another level. If he could just perfect his mimic of Wilson's escape act he could be truly dangerous.