A few more things to add to Dave's reply:[li]CM15a is a USB connection CM11A has a serial port connector[/li]
[li]With the CM11A you'll need an additional transceiver the CM15A has one built in[/li]
[li]There are many software programs available for the CM11A. Not so many for the CM15A, yet![/li][/b]
[/list]
The real key to deciding which one you want to use, is to Ask your self:
What do I eventually wish to do with it?
&
Will that controler do it?
The CM11A has many limitations