It doesn't block the flow, it shreds the tail as they pass by. So they can no longer swim up to fertilize the egg. You still ejaculate all your sperm. And there is simply no way a doctor is going to "accidentally" block a vessel when doing something that is an outpatient procedure. Anymore then they'd "accidentally" chop your balls off when giving you a vasectomy just because they happen to have a sharp object down there.
I've been watching this since 2010 and I've donated a few times to the foundation funding the studies. I would have killed to have this in my youth but sadly I'll probably have a couple kids and a vasectomy by the time it hits the market. It I'm really surprised that the Bill and Melinda Gates foundation hasn't gotten behind it as it's non hormonal, reversible and costs pennies. Hell I'd make it free to any country in the third world that wanted it.
