Terrible customer service and they don't take responsibility for their errors
The software and commissions are good, but beware everything else. Connectivity is poor and customer service is non-existent.
Interactive Brokers made an execution error on an option contract for me (it turns out the option contract did not exist!). They then magically reached into my account to "reverse" the incorrect transaction, leaving me with the hedging stock position. Needless to say, they took the winning position and left me with the losing position, down EUR 1,000 on the trade, instead of up EUR 500 with the option contract.
To make matters worse, my complaint has gone completely unanswered for two weeks.
UPDATE 2021-04-01: Interactive Brokers finally responded to my complaint, and rejected it. It is apparently their policy to execute fake trades [i.e. product does not exist] on your account, and then after reversing the fake trades, they leave you to clean up the mess of the hedging trades [which are real] at your own cost! I am now forced to contact the financial ombudsman for their assistance.
March 2, 2021
Unprompted review