i used this feature quiete often now, and i noticed one "annoying" thing about it: you're limited to one setting only.
idea: make a submenu, in which you can define a few presets (fisheye,WA,tele) and one can set values for each entry. this submenu can then be added to the "user menu", that makes switching super easy and super fast.
another idea is to AUTOMATICALLY engage a preset in specific situations: if you zoom (the built-in lens) to the maximum position, the tele lens setting will kick in. if zooming to WA, the WA setting (or fisheye) setting will kick in.
when you do a photography session and you know that you ALWAYS use the extra tele lens in conjunction with full tele zoom (same applies to WA) this is a handy tool. maybe it can be locked to certain zoom levels.
with a submenu you can also do the following: add a checkbox if value should be reset to 100 if cam is shutdown or restored.
also you can create an icon that shows up if you override the factors (maybe a WA and a Tele icon) so people easily see if it is engaged.
let me know what you think, i can help creating this stuff. if you dont wanna do it, i can do it on my own, supposing people find it useful.
edit: and yes, would be nice if this was written to the image exif data.