II have the realflight 5.5 RC simulator.

I use it to practice my orientation skills without bending real hardware.

Whne I ordered my ArduCopter from Jdrones I started looking for a simulator that had a quad.

The visual presentation of a Quad is very different and I wanted to practice flying it before flying the real thing. About the same time I became aware that the realflight expansion pack #8 had a quad so I ordered it. The expansion pack was delayed and arrived 2 weeks after my first quad flights.

See:

The quad is so much more stable than the helicopter that flying it is easier and the simulator was not needed. It also helps that it is less imtimidating so I fly the quad closer than than I fly the helicopter.Given that I no longer need the simulator.,

My general impression is that its a good simulation of flying the quad in stabilize mode. The simulated quad is a tiny bit more stable that the real thing, but all in all I'd say its a good simulation.

If you want to start with a quad and have never ever flown RC before Id strongly recomend the simulator.