I sailed an Fx-One for a couple of years and I was very happy with the boat.
But in the end it's just where you want to use it for.
- just cruising : excellent boat, you can rig it for 2 and use the spinny and even a jib.
Mind that the Fx-One is not a catamaran to be beached, the hulls are to be handled with some care.
- racing : in Europe there are some sailors racing the beast alone. Racing is a lot of fun especially with the spinaker. The A-class is a bit bigger (and has it's own class), but no spinaker fun.