RE: Am I Making A Mistake ??
Its all about options, In a choice between the 7C and 9C the 9C is the obvious choice being a far more capable Tx than the 7c.
If the 7C is the 2.4 only version and you do acquire a 2.4 module for your 9C then it has agine more options on what kind of Rx's you can use.
Even if the 9C/2.4 module combo ends up costing a bit more than the 7C the 9C reamins a better value, better features and an obvious choice.
Even another option that is open to the 9c over the 2.4 only 7C is that you have the choice of using the Hitec 2.4 system module and Rx if you choose. Key advantage is the Rx's are and will remain considerably less expensive which adds up as you add aircraft to your hanger. This system is in my opinion even better than the Futaba Fast system. It is the only one which will give you a low battery warning of the airplane pack While in flight. This just did recently save my butt in flight when I made an error in my charging routine the night before.
Yes the 9C with a 2.4 module is an obviously wiser choice.
John