Out of the eight converters Ive downloaded, I found it easiest to remove/add units on this one, because I didnt have to go through settings or menus to find the options.
However, theres not enough customization otherwise. You can change the seconday color of the app (pastel red/purple/blue/etc), but neither the text colors nor the main background color (white) can be altered. In my opinion an unwise decision was made to color the text displaying the units in gray, making them rather difficult to see, especially since the font *size* for the unit text is the smallest in the app.