Male Contriception: a new approach

So I was browsing through some articles on the BBC Website and I say a little article that went a little something like this:

Male 'contraceptive jab' closer

Monthly injections of testosterone lowered sperm count

A male contraceptive jab could be as effective at preventing pregnancies as the female pill or condoms, work shows.

The monthly testosterone injection works by temporarily blocking sperm production and could revolutionise birth control, experts believe.

This seemed like a very interesting concept. It would make sense that messing with hormonal factor would lead to decreases in sperm count from what I have seen in Physiology classes, but in my opinion it seems like a bizarre idea. Wouldn't there be too many side effects from the increase in hormone? I wonder if this is really feasible. I mentioned in the article that out of 100 men that underwent these injections only 1 instance was a child conceived. Is it bad that I am quite skeptical??