Well, Odri is quite rare, I've only seen it once, but it's on a TV reporter so you hear it all the time. Nensi however is quite popular.
While -o names are generally male, there is no one way to define a male name (like -a for female, although we do have male -a names too), you just KNOW they're male. It's mostly by eliminating the -a ending names (with those few traditional exceptions -like
Matija,
Ivica,
Ilija,
Andrija, Borna) and then you get a male name.