Only makes sense for investors. Traders with several trades per day turnover will pay more in the end through inferior execution. Also you don't have access to tws' pro version by going this route.
Delayed fills for starters. Your order is sold and may sit in a dark pool or get aggregated or re-routed multiple times. That's just for starters.
This is constantly repeated like its gospel, and proof is never given Let's see hard proof your order is not filled at the best bid/offer in a timely manner If there's no proof forthcoming, then I will assume the folks pimping this nonsense are full of crap, 2000 posts or not.
Who would benefit in giving you the proof? Definitely not your broker. If it's not an issue for your type of trading, there's nothing to worry about. I suggest you read those 2000 posts, might just learn something new.
I'd like to just add to this by not going with pro you basically have no access to all the best features of IB. In particular their API, which is worth paying the commission by itself. You can more or less assume you are going to get inferior execution if you're not allowed to choose routing or are left to choose only from inferior routing choices. To quote the website itself:
I agree, what a pathetic way to participate in the zero movement. What I would do (and I know they will listen to me) is keep everything the same except: 1. Add ZERO route which is like SMART, but cannot be customized in any way. Only this route gets zero commissions. 2. Add the free CBOE One data feed, but keep the option to upgrade to paid feeds. The way it stands right now, I see no reason to choose IB for zero commissions. Obviously, they have lots of other perks, but I doubt zero commissions crowd care about those.
Well, all I can say is that Cheap Charlies always get what they deserve. I am absolutely sure that soon enough all those accounts with zero commission will get charged much higher stock loan fees and margin loan fees. And why not. Brokers are not stupid and go bankrupt over Cheap Charlies. It's those intransparent fees that those guys will pay up for. Brokers may in the end of the day actually earn more than before.