I've done this many times and found it flawless..just cut clones off them, tag em'and pop them into a clone machine and set with 12-12, For me they'll show their gender in 7-10 days...and some show gender even before they show roots.
If you choose, let the clones root out fully and use them yourself or gift them out.
just as a side note...I've had great experiences with fem seeds...no herms or weird shit but note that I have only used HSO and Dinafem fem seeds. Some of the reading I did stated that Dinafem does a lot of fem seed production of other breeders regular seeds. Dinafem is a good company IMO.