Are Earnings Limited?
One of the core benefits of spread betting is that earnings are totally uncapped, with the potential for traders to ride the market for as long as they like. This feature of spread betting has made millionaires, and makes spread betting inherently attractive as a trading style, with every single upwards point an extra multiple of your initial stake.
And traders should have no fears about their brokers capping winnings - remember that brokers have your position covered, either through other traders or hedging on the futures market, and so prefer traders to succeed. After all, successful traders are likely to place larger wagers, and execute more frequent trades, which will all contribute to the bottom line of the broker.