Yea I got this gear as well for my CP PRO. Although you are right it is not built for a blade you can accually make it work without any modifications. Here is somethings I did to make it work:

The shaft is too long. What I did was make the shaft stick like a half inch or so bellow the gear. Be just having it go through the gear and stick out you can make it work with the appropriate pitch etc.

As for the top hole being too small I have found that a paper clip fits perfectly. So I just cut a peice of a paper clip and then bent it to hold it in there a bit better.

Only other issue I have run into is the shaft wanting to slide a little up and down because I can't fit that second collar above the gear and still get good gear connection. So I have it so it rides right next to a couple zip ties. When the shaft shifts it will hit the zip ties which push it back down. So far I have not had any issues with this, but I am sure it causes some excessive friction.

Overall I am not very pleased eather. I plan to do something else in the near future. I like the auto rotate, and I needed a new shaf (I bent my old one). And I am willing to live with it since it is working fine with these modifications.

Hope this helps, I am intrested to hear what others did.