I like the way it sounds but not the way it looks - I do find it a little masculine. Also I would avoid it in a non-French-speaking country because people are definitely going to pronounce it wrong.
I know one Manon, who is probably about 15 now. She is French though, so it's different. Also she has a little sister called Justine, which I adore with the French pronounciation but not the English!
Favourites: Eve, Alice, Norah, Isla // George, Charlie, Arthur, Oscar