Does it have to be a 355, and does it have to be Eurocopter?
They are not renowned for their lifting capabilities, though I rather like flying them myself. Their only real benefit as twins is that they are small enough not to annoy the neighbours, and yes, if you get anything Eurocopter make sure you can either sit on the ground for months while you wait for a new engine (and gearbox) or have a spare.
As I understand it, the FX is simply any model of 350/355 with a new wiring loom (sorely needed!) and some new instrumentation. Typically shaves about 100 lbs off the AUW. It's not a separate type as such.
phil