If I get an erection and put the constriction ring on will I maintain the erection for as long as I want even without stimulation? Also I have problems with blood flow and circulation, so how dangerous would it be for me using the ring?
Yes, guys use them to maintain there erection for sex. I wouldn't say for as long as you want, but rather need. I find cutting off the blood flow gets uncofortabke after 10 minutes.
If you have peyronie's, look into not using the rings a little more. It can result in deformaties such as hour-glassing.