I've been hesitating to answer because I don't know about Camtasia for the Mac.
I was under the impression the Mac version had all the bells and whistles as the PC version.
(The Mac version was recently released so if you haven't checked the site recently you should)
The PC version of Camtasia simply rocks.
It does a lot more than just screen capture and has had a very recent update released too.
If I was rich I'd buy everyone here a copy of Camtasia to use with A:M. It is that useful.
My primary dilemma these days is finding the time to use it.
Edit: Yes, it looks like the Mac version is limited but improving.
As I read into it more however, its not clear what those limits are (if there are any).
Knowing what I know right now, if I had a Mac I'd purchase Camtasia for it.
I think the price may be mostly to get their foot in the door.
If in doubt, I'd contact them and see what they plan to do with it.
You can download a free trial of Camtasia for the Mac (and PC)... what have you got to lose? http://www.techsmith.com/camtasiamac/free-trial/