The unit settings page was a little confusing at first, but I got the hang of it just by playing around with it. My sense is that you can probably leave the layout as is and see if the documentation is adequate. But if you are still getting feedback about the settings layout, you should consider adding headers (maybe in smaller font) to delineate the sections on the left-most column on the page. Categories Area Length Saved Conversions Fahrenheit-Celsius Mile per Hour - Kilometre...
One other set of conversions you should consider implementing is clothing and shoe size conversions. I think that the tricky thing with that is that they may not have set conversion factors--I think you would have to rely on conversion tables for those cases.
Otherwise, great job!