Above mentioned are brokers. Do you need to have an account with either one of them in order to take advantage of the free real time data for Ninja?
Wrong. Mirus will set you narrow limits. Then you will have to go live. (Don't know about Amp's policy)
Mirus gives 1 free month. You can keep changing e-mails every month to ask for a new free demo, if you do not have the minimum to open live account. Btw, their minimums are very low.
Red Duke is correct. It's not difficult for futures. Open demo account with AMP or mirus and you can trade live futures on a demo account. When the demo expires, you can register again with a different email address, or just send them an email and say you want longer. No way in the world will they say 'no'. It is trickier if you want to demo trade EQUITIES using live data, though, In the past I did find some good ones, though (as previously mentioned)
The bold text is absolutely wrong (regarding Mirus, don't know about AMP). Telling you this just in order to not run into a bad surprise some day (as I did).