Hans,
I trade with PointDirex. The difference in the .0075 vs. 1.2 cents per share fees relates two the two platforms currently available. THe one for 1.2 cents is a level one platform with direct access and proprietary smart order routing technology. Since PD finds liquidity for you via the smart routing, different sources of liquidity will be accessed depending on circumstances. The 1.2 cents is flat and includes all ECN fees etc., that PD will incur to find the liquidity.
The other platform is the more professional DIrex pro platform. It has separate pass thrus for all the ECNs and SOES etc. THey have direct connections to 8 of 9 ecns. This platform is very similar to Watcher (even looks a lot like it) so you will recognize this technology. It has been around for 3 years or so, but like the watcher, was previously only available on PD trading floors. In November, they rolloed out the internet ready version, which is what I use. Considering it is a new platform in terms of being available over the web (my understanding is that even though it looks the same as the original, the fact that it was made to work over the web meant re-writing much of the code), it is remarkably stable. I have no complaints whatsoever. I also use RealTick still for charts etc., but Direx Pro for executions is simply amazing.