Hi, I've just this week become a customer of NinjaTrader Brokerage.
I cannot comment much on the trading side as yet, account is just funded and I will be trading MES and MNQ.
Account signup, funding and platform configuration has all been very smooth, no complaints there.
I'm on their free edition at the moment, but think I need to take a subscription, as the free version does not even allow placing of stops and targets with the submission of an order, as far as I can tell. Which is really a bit meh!
Otherwise, looking forward to getting started on it.
TDUK