I have had a good experience with eChineseLearning. I needed to prepare for the IB Chinese B SL exam, which is roughly equal to the HSK 5. I had only taken two years of Chinese in high school before that, so I was having a really hard time keeping up with the other students in my class, who were mostly Chinese themselves. My mom suggested I try online classes, and signed me up to do lessons three times a week. Having someone explain everything to me one-on-one really helped. I ended up getting a 6 on the exam - which is pretty good considering I didn't think I would even pass at all for a while. So I would definitely say it was worth it.