I think the last Mikey Mouse operation lasted about 4 weeks prior to being driven back into obscurity.
Major benefit to prop firm: No need to risk MTM election with IRS and set yourself up for potential scrutiny/validity to trader tax status if your trading volume is questionable. Trader tax status is still an extremely gray area of which even the IRS cannot provide 100% definition of what qualifies. With a prop firm you receive a K1- and hence 100% eliminate wash sale rules as well as accounting for your trades on a schedule D.
Tax treatment is a consideration. When I run any business, I care about risk/reward and my end of year net. With a prop firm I'm concerned about the risk of commingled funds. I want be concerned only about my trading risk. With a prop firm I feel like I have to keep my volumes up and be concerned with their rules. I want to only do trades I have an edge, and follow just the rules of law. If I require a prop firms capital to trade, all this makes sense. If I have the capital to trade without them, it's not for me.
Once again I'm going to state for the record, I've been in the business for over 10 years in both Chicago and New York. I know traders at almost every prop firm in existence and the pressure to trade has NEVER been an issue to any traders I have talked to. Please keep in mind I have no incentive to stick up for competing firms. I'm telling you this because it's true. Is it possible there is some sub LLC out there that might pressure their traders to be more active? Sure. But I would never recommend anyone going to a sub LLC anyway.