The porro design of the Mountaineers allows for slightly better light transmission by using bigger reflecting surface areas of the glass inside while still keeping the outstanding clarity.
Isn't there less glass in general with a porro prism design...in comparison to a roof prism? I have read in several places that a $100-$200 pair of porro prism binos is equivalent to a $400-$500 pair of roof prism in terms of light transmission, clarity, etc... because of the fewer glass lens/mirrors that light must pass through. Maybe you would want to comment on this a bit?
In reference to alloutdoors comments, I do agree that the lower power/larger objective binos would be ideal for many close range viewing situations. However, I think many folks are faced with both short range and some long range glassing that would require both a large objective for better light transmission and a slightly higher magnification to discern more details at farther distances.
Two examples of this, in my case, immediately spring to mind. One, our antler restrictions here in PA now make it critical that we count points. I have been faced with at least two occurrences where my 10x binos really came in handy. Going to something less than 8x probably would not have yielded the same results in my opinion. Second, and you guys are probably going to laugh at this, but I use my binos also to check the number of hits on Stealth game cam. I have it placed in a location where I can glass it from a distance without setting off the sensor and taking a picture of myself. Plus, I do not leave scent in the immediate area of the camera.
As I said, each has its place but it is difficult to just go with one size magnification or objective lens diameter to fit all situations...in my opinion.