This is a question dear to my heart, and I will tell you my experience (I have posted it before, but here it is again.)
I am with IB for about two years. I trade 98% listed and 2% NASDAQ.
On NASDAQ, I wouldn't hesitate to use IB. The executions are lighting fast as anywhere I have seen. In addition, if I am the best bid/offer, it will be displayed in the L2.
_HOWEVER_, on Listed, maybe one in a thirty times do I see my bid/offer displayed when my bid/offer is the best bid/offer (BTW, I know of the uptick rule, which could cause your offer not to be displayed in those cases.)
I have two different datafeeds, with T/S displayed so that I can see the real bid/offer on a stock (IB quotes STINK)
I got so infuriated one day, I called the IB help desk and demanded that one of them stayed on the phone with me while I showed them how my bids/offers would never show up as the best bid/offer in spite of the fact that _I_WAS_THE_BEST_BID_OFFER_. I did this with several stocks to prove that it was not the stock. To the amazement of the IB help guy, he did not understand why this was happening. He said he would look into it.
A couple of days later, I got a call saying that someone had talked to one of the specialists and that his answer was that he doesn't "always" have time to update his quotes.
Now, and here is my belief on this:
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The only way you or I are ever going to find this out is by having prop experience. Even better, it would be great if when at a prop firm, we put in identical orders at IB and at the prop firm and compare.
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(Unfortunately, I do not know how prop firms treat this. From what I understand, they want to know all the accounts that you have when you trade with them. This may be for other reasons though, and it may be OK to have them as long as you tell about them. In addition, many if not all prop firms do not allow connections to the Internet from their computers, except for their execution systems.)
Therefore, I have to agree with RTHarp above and Gene - you get what you pay for, for sure.
In the meantime, IB is a great platform to get your feet wet trading, or just fine for swing or longer time trading/investing. I don't swing, but do invest with an IB account and it works OK for this.
However, IMHO, you would be _CRAZY_ to _SCALP_TRADE_ with size with IB, or strategies that are time critical at IB.
nitro