The big kicker on flow bindings is the rear entry system, depending on where you shred this may be a big deal or a minor detail. I personally ride a small mountain with 2 min runs so you can see how speed entry appeals in those situations.
The downside to Flow is a lot of their new tech that hugely improved their men's NX2 line is not present in the women's bindings. the NASTY strap tech is awesome.
As far as the flex on the bindings, the stiffer the binding the more responsive it will be in all mountain conditions. Soft flex bindings and boots are usually preferred for park while stiff binders and boots are for speed
If your already prepared to spend 130$ on the Flow Gems but rear entry isn't a big deal, i'd check out the Ride Fame 2013 binders on Evo
ekb18c said it. you could save some cash and just hit up a decent craigslist. if you "need," a new pair of bindings, whatever evo, backcountry, etc have on outlet/clearance mostlikely will be good enough for your first pair of bindings.