If you were moving up from a 6ch micro (GeniusCP) up to a 450 Sport, do you still need the cross bars and pingpong balls?

depends on how good you were on the micro...
they cost less than 10 bucks to buy and might very well save ya 20 in a silly crash

I always landed on my skids, even when i used the throttle hold (That was pretty cool, was about to run into a tree, i cut the throttle, and it landed right side up). The crashes i've had has been with the blades hitting a wall or something. The 3 axis gyro on it does a very good job.

I would until the heli was sorted out ...

There is not just a learning to fly curve , but a set up curve [ learning ] as well .
So until you have the hang or have actually set up the 450 correctly , the trainer add on is a safety net .