One thing I forgot to mention, when you are using Realtick in demo mode (whether it's the 1-2 days they allow you without funding, or after you've opened/funded an account and requested it), there is a severe limitation in my opinion. Sure, you can try out most of the features of the software, but the order-routing is limited to one method only, called TAL-X. I asked them about that and they explained it was an internal system they had setup within their servers to allow you to simulate real trades. When I protested that it gave me no exposure to how effectively (or not) their system routes thru various ECN's, Specialists, MM's, SOES, SelectNet, etc. they essentially told me "Too bad, that's all we've got".
So do the demo if you want exposure to the software, but be aware that it's lousy for simulation trading.