Take for example xTrader, which costs $1500 per month (pro version) and is popular among professional traders, and ninjatrader, which you can buy outright for $1500. What justifys the price difference? I know xtrader is known for its quality DOM, but at the same time there's the option of buying the jigsaw DOM add-on for ninjatrader which is actually better. So apart from the DOMs, what justifies the price difference? Faster execution? Special features?