I am wondering whether there are any male contraceptives that are:

1. Reversible
2. Fairly convenient, on the order of taking a pill once a day
3. Do not need to be used at the time of intercourse, unlike condoms
4. Minimal side effects
5. ONLY effective enough to be used as a "backup" to a primary
contraceptive, such as condoms

Researchers are looking for the ideal male contraceptive, which could
be used by itself and still be highly effective. Until they find
something, wouldn't less effective contra. still be useful? Isn't a
50% reduction in sperm count better than 0%?

I thought I'd ask here before starting to comb the reproductive
journals.