Lower commissions and more flexible leverage plus solid API offerings are all valid reasons. Thing is when I contacted a 'prop' firm previously, the commission quoted was higher than IB plus software/data fees, making me wonder why the heck anyone would consider using them
For the leverage. When I spoke to Rob Friesen (Bright Trading) back in 2014, this is what he told me, straight up. Leverage is the only reason. The prop firm business model is renting capital to undercapitalized traders. This rent is paid in the form of profit split and/or higher commissions, fees, margin interest, etc. At least that is the business model of the legit ones A lot of the prop firms I was looking at back then eventually disappeared and/or turned out to be scams. Nonko, anyone? In hindsight, sticking with IB was a great choice for that reason alone. Plus I never did come up with a strategy that could safely use more leverage than portfolio margin anyways (~6x)