I'm afraid i can't be so much objective with this question, but doing an effort, i'll say i go along with Marie-Hélène answer: Italki just works if you're constant and selective. Maybe is not the best way for learn a language (mostly if you're beginning) but it works for keep in touch with the language(s) that do you want to improve and for prevent can be forgotten
So... what is my score for Italki?? well, takin' in noticed that:
-The chat works like a pedal boat
-The few times you have the "big lucky" of make use a chat that works (more or less) is for found to yourself repeating 100 times the answers: "What is your name" and "Where are you from"
-Teachers can be any native bored
-The language groups are only crossed by tumbleweed (these rolling plants of Western films)
-the Answers section is mainly used for write the first bullshit that comes to our mind (me first)
-and so on...
my score is...
more than 10.
Why? Well, i've had a lot of funny moments here besides to have found another great things...
as I said: i can't be objective