I think it's impossible to compare these things accurately but women have been taking the pill for more than half a century. It's been proven to be relatively safe and reliable for most people. Something for men would be great but I'm certainly not going to risk future fertility with something that new and untested, particularly when my partner has a much more tested and safe alternative. On top of that, men have a very simple, effective, and safe option available - condoms. They have their own downsides but they don't outweigh the risk, pain, and anxiety of an injection in the scrotum.