going lefty with the mouse makes a LOT of sense. Unfortunately it means a fairly steep learning curve, I think, for us lifelong righties.
i do indeed write with my left hand but i'm not sure how much this weighs when considering that i too have used my right hand for the mouse all my life. i only made the switch 3 days ago and it feels so natural. i think it has less to do with switching hands (even if i am a lefty) and more because of a very ergonomic / natural set up that is comfortable.
the only time i'd probably return to the conventional set up is for high precision stuff like gaming. however, that has more to do with needing more improvement in the mouse shape. it's easy to click the bottom button and i know the manufacturing has improved on that in the revised design for which they only released the right handed version as of now.
so yeah, for regular "office" work, making the switch shouldn't be so bad. see if you can get a used left handed mouse (preferably vertical) that you can sell back if you don't like. i know you've tried various ergo pointing devices in the past when you had rsi.
yes, the standard will cover only the numerica pad portion of the 1391401. its actually a good thing that you emphasized and pointed this out. it was this exact set up that was not good enough for me in the beginning of this thread. so i guess that is emulating a model m mini. personally, i like the "fit" of the height adjustable better than the standard. i bring the mouse as close as possible without covering the delete button. of course, now i don't care anymore thanks to the clever layout of the mx11800 (very intelligent to bring the delete button close in the middle) and since i've abandoned mouse bridges.
if you have any other questions about left handed mice etc. let me know! definitely worth a try. even though i still use my hand for gaming, it's nice to shift the workload to my left hand. great relief.