I just made the transition from two strap to the Flows (NXT_FSE) and I'm a big fan.
They are a little spendy, but since you're already looking at the FRX, i gather thats not an issue. The combination of comfort, ease and great heel/toe response makes them hard to beat, IMHO.
May take a couple runs to get used to the different feel of the strap fit, but right about the time my feet would have started hurting, I got used it and was a convert!
I think they're great but to give a balanced opinion, the weakness in my Flows are the ratchets. They're not as smooth or responsive as many others, but since you don't need to use them once you set them, its a minimal issue. Good Luck.