I don't like the requirement of running their little jar package for the actual order entry. The CTCI requirement to avoid the jar package (TWS) is not too bad for a dedicated connection.

What really bothers me are these people saying one place "we're compliant with FIX 4.1 and 4.2", then later somewhere else, "We have pieces of 4.3 and 4.4 protocols" and then, "we have proprietary extensions to the FIX protocol." I suppose that means as a developer I'd start with FIX 4.2 and then merge in some of the 4.3/4.4 features. The proprietary 'ambiguities and extensions' part will probably be the most annoying, least documented and implementation specific part.

The functionality from 4.3 is probably swap support.
The functionality from 4.4 is probably multileg orders and position reporting.

If IB and FIX are used, we'd probably save time by supporting CCTI at $100/mo. I am not thrilled with the idea of using FIX for quotes and TWS for orders.