You actually can see "institutions" trading real-time. Who else is going to walk into ES and sell 500 back-to-back, or ZN and sell everything on the bid, offer lower, and sell everything else on the next bid? You and I don't have enough capital to put on even 1000 contracts in ZN. Somebody with large pockets does, and that somebody is a big player.

I definitely agree that order flow is tough to backtest. That's where the feel for the market comes in. What's your market of choice? I bet you can tell me when the action looks bearish but feels bullish, and the reverse. It's all about knowing your product and the way it flows.

There's no "proof of concept" in order flow. You aren't going to buy a system which flashes green and red lights to buy and sell, but I'm guessing that you already know that. Those things exist, but every last one of them is a sham.

You can see what institutions are doing, but the tough aspect is predicting what they will do. That's what trading is all about. Order flow tools help you see when large, significant, market-moving size is trading and aggressively clearing prices. It's then up to the trader to decide what to do with that information.