I don't like them really at all, and would never rely on them or even think of them as a safety feature... Keep your fingers the heck out of the way of any edge I say! (one reason I'm not real fond of lock backs, since you Can Not release them without having at least one finger in the path of a then free swinging blade.)
A hazard is mostly how I see them. On normally sprung knives, less so, but on bear trap sprung examples its terrible. Tends to cause the blade to suddenly snap to the half stop on opening, pulling the blade suddenly away from your finger, or out of its grasp if pinch opening; Too much uncontrolled blade movement close to fingers. If it doesn't cut you as it jumps, then depending how your reflexes are, when you recoil from the then fast moving blade, you have another chance to get cut. Same for any try at a controlled closure. No thanks.
I do tend to be able to ignore them on smaller knives, for instance never notice it on my Peanuts. For some knives, there is a rounded corner to the tang, more of a normal tang cam end with a smooth transitioned flat area on the end... thats OK most of the time because they don't jump around opening or closing, and can be ignored.
But perfectly square cornered tangs to give a half stop I consider a defect, and a cutlers trade failure. One reason I refuse to risk buying another GEC knife. Their combination of square corners and bear trap springs are a royal pain to deal with.