Groin Protectors and Low Blows

How much protection do these boxing groin protectors actually supply? I've been to a boxing gym and actually used one (a Reyes I think) and I thought the protection that this thing gave was superb. The cup section had a hard plastic surrounded by padding and felt comfortable. Although I've never been on the receiving end of a low blow with the protector, I fell it would do a great job in protecting my groin area if that situation came about. I see from time to time fighters go all out with pain when they sometimes receive a tap in the groin and not even a hard shot. Sometimes I see fighters take a hard shot low and brush it off like it was nothing. For those of you who have boxed with one and got hit low, how much support did it actually provide? How much acting do you think fighters actually put on when their hit low?