Quote from riskarb:
Reliability and fill quality. TOS can't touch IB's spread/combo algorithms. TOS doesn't offer VaR. TOS is far more costly. TOS doesn't have 1/10 of the product offering, nor futures.


Charging margin on reversals for european options is pretty annoying. For American, though, it only makes sense. Their formula seems pretty reasonable.Quote from ssmegner:
Same underlying, same strike: short stock + long call + short put. IB wanted margin on the short stock position plus margin on the short put.