FWIW, we are a sponsor too and normally don't weigh in on questions to a competitor on their threads
Direct routing is not more expensive. Look at the commission structure. You can direct route as you wish. However, I recommend SMART because it should improve the chances for an execution. Unlike other brokers, IB doesn't forget about your order once it gets routed to a venue. We constantly monitor your order and re-routes all or part of your order attempting to get the best fill (and this includes passing on exchange rebates when available if you chose the tiered structure).
IB does not sell order flow to TH. SMART routes to the best available execution and external audited reports consistently show IB's SMART routing getting much better price improvement and fills over the industry.
https://www.interactivebrokers.com/en/index.php?f=1685
I'll start with Barron's who quotes:
Fequent Trader's 1 Monthly Costs
Barron's estimated a customer's monthly costs at each of the 16 brokers in this year's "Best Online Broker" ranking. Interactive Brokers was the best deal for both the occasional and frequent trader.
Lowest
Interactive Brokers $847
eOption $881
Just2Trade $1,163
Lightspeed Trading $1,200
SogoTrade $1,500