Hi Tom,
I have the Zeiss 6 x 18. I like it. It is 3 and 3/4 inches long. Fully extended it is about 5 and 3/4 inches long. It comes with a small, well designed, zippered leather case and lanyard.
I think that 6x is the lowest power for practical all around use. 4x would not be strong enough for me for overall general use and anything much more powerful would be too hard to hold steady. As it is one has to experiment to find the best way to hold a monocular steady.
The 6 x 18 focuses with a draw tube located at the objective end of the tube. For distances beyond about 10 feet focusing is minimal and the draw tube requires very little adjustment.
With the draw tube fully extended I have been able to focus down to about 9 or 10 inches. At this distance the field of view is very small and it can be hard for me to hold the monocular steady. Good lighting of the subject is also helpful.
It has long eye relief and it's rubber eye cup can be folded down for use with glasses. Pressing it up to one's glasses can help steady the view. In this instance I think that the 6x might be more appropriate for sports unless you prefer a wider field of view and then the 4 x 12 might be more useful.
It is an all purpose handy optical item to carry around with you because it is versatile and will fit in all but the smallest of pockets. It can be used at a concert or for a quick look at a scenic view, bird, animals, bugs, flowers etc; but for sports events and concerts it's not as good as a compact 8 x 20 binocular IMO.
Hope this helps,
Bob
PS: I have used my Leica 8 x 20 Trinovid at concerts and they worked very well for me. I think they are easier to hold steady than a monocular at that kind of event and not much more intrusive.