I should expand on this a little...
My interest here was to see how B&W images that result from using just a single channel of pixels compares with downsizing a colour image converted into B&W.
Also in this test is to see if there is less chromatic aberration due to different wavelengths focusing at different locations on the sensor.
Finally, it gives me a good sense for how much sharpness I should be applying in LR. Before being able to look at the per-channel images, I was just guessing about how much correction to apply (if any.)
The catch is that the output from 4channels.exe does need work (brightening, etc) before it is really usable.
As an example of the difference, I've included 3 attachments. One is just the red channel from the file, one is colour (no adjustments) from LR, and one is after colour to B&W (no other adjustments) in LR. Of course the catch here is that the red channel is 1/4 of the size of the other two.
Well, on your first point, of course there is no comparison because a conversion to B&W relies on all three primaries, which inherently must be a very different result from that given by any one of the constituent primaries in islolation, so not clear what's the purpose behind it.
On the second point, CA is the result of what your lens does when the image is exposed and LR has profiles and manual controls for correcting it very efficiently, so again, I may be missing something but I have trouble perceiving the value-added of the difficult approach.
On the third point, there is excellent instruction available for LR4 on how to evaluate and control sharpness using the grayscale rendiition of the image that you can trigger easily when using the sharpening panel tools.
So I remain somewhat mystified about the usefulness of bothering with the hard way, but of course an interesting intellectual odyssey from which something useful could emerge - so I'm not knocking it, just wondering about value-added and usefulness.