I am male, so I can't actually make a punishment bra. But I have experimented with punishment collars.
My first experiment was using a prong collar - similar to a choker collar, but with solid metal, blunted prongs that bite into the neck when tightened. I bought one, put it on, cinched it up, and padlocked it for a couple hours - and sadly, it was not very punishing at all. Eventually, out of boredom, I padlocked my shackled wrists to the ring in front - and discovered that even the slighest pull on that ring caused substantial pain and discomfort. Unfortunately, after I was done, the red marks didn't fully go away for a day or two.
I ended up making a punishment collar similar to this punishment bra, by cutting a belt down to the size of a collar and punching a few holes in the leather. The spikes I used are actually thin, quarter-inch-long nails, pushed into the leather from the outside and held in place with a drop of super glue. I used a steel file to knock off the ultra-sharp points, for fear of injury. Although the spikes are sharp and prickly...wearing it is not as punishing as I hoped. Even after cinching it tight and waiting for three hours, there was nothing but mild discomfort.
Perhaps I need longer nails.
Life is like a set of shackles. They may be cold, restricting, and unforgiving at times, but you can still have loads of fun.