Rated 5 out of 5 stars
It works flawlessly and it saves a lot of frustration for non-latin users.
As I am using a cyrillic keyboard layout along with the standard EN, I used to make a lot of Shift + Alt's to change layouts, but the most horrible, terrifying thing is when you don't and you've already entered a search term that looks like this "и кноњ њхат ѕоу дид ласт суммер“ or a web address like this "мовиедескбацк.блогспот.цом“ and then you would have to type it all over again.
With the add-on you can always use your primary keyboard layout for tweeting or chating with friends and when you need to search or go to a web address just start typing in the awesomebar and it's automatically latin letters.
One thing though, there should be instructions how to set it up to work with every keyboard layout. It's an easy set up but a lot of people seem to think it works out of the box, with no modification whatsoever.
Also it doesn't seem to recognize visited pages this way and auto-fill the address, but what it does is way beyond helpful to count this as a disadvantage.