When you get a "shake", two things happen.
1. you collect ECN rebates on the in AND the out
2. you make the spread (of at least 1 penny)
Obviously having a lower commission, is ideal...and the way to get that is typically to go to a proprietary trading firm such as Title Trade or World Trade...but there are a lot out there to choose from...all with different deals so you should shop around.
However, it is important to realize that the shake can be completely customized, so for instance instead of just making the spread each time, you could set it up to make 2 pennies, or 5 pennies....this would allow you to use this algorithm with a higher commission structure and still see some of the benefits.