(0) clamshell mode when connected to an external display;
(1) as a laptop.
If (0) is the case, I use mouse and keyboard but sometimes I miss the fact that I can just scroll quickly on the MBP's Trackpad. However, pressing on the Trackpad for long hours isn't fun either as my fingers get tired.
When I started using laptops more frequently (because by then I was doing a lot of consulting, and therefore using laptops), my CTS went away. I figured out it was because of the trackpad.
When I went back to more static computer use with an external monitor, I also made sure to have an external trackpad, and my CTS still has not returned.
These days, I do have a bit of pain issues with my right thumb, and the wrist braces for De Quervain's tenosynovitis are the main thing I have found that will help. But to be honest, at my age, it could just as easily be arthritis. I will check this out with my orthopedist to be sure, but for now the wrist braces work when I have pain.
So, yes -- the Magic Trackpad in particular is a key part of what allows me to continue to work and be a contributing member of society.
Personally, I haven't noticed any fatigue. I also do have tap to click mode on which I feel helps.
I doubt it makes me more productive. For me, the best way to describe it is that I never think about it when I’m using a trackpad on a Mac.