I actually find the reverse courses very useful. I have worked with the reverse courses in many languages, including Chinese, Japanese, Spanish, German, and Portuguese.
Perhaps my experience is different because I am experienced with language learning and have a good sense of how I need to approach learning a language to make it work. Chinese and Japanese would be my fourth and fifth languages, respectively. For German, Spanish, and Portuguese I did the "forward" courses first and then went back to the reverse courses for extra practice.
For the Chinese course in particular though, I want to emphasize, the course is not good as a standalone course. You need to master Pinyin and pronunciation before and get a good input method set up before starting the course. Learning Pinyin and pronunciation are hard. I recommend consulting multiple sources. I also recommend starting to listen to some Mandarin Chinese probably several months before you start trying to learn. Don't just listen passively but listen actively, paying close attention the sounds and tones and structure. Keep in mind, it's not just the tones that make Chinese hard, the consonant sounds are VERY different from English. Don't be deceived by things written as familiar letters like "d", "t", etc. There are significant differences for many of these sounds, from English.
I also recommend getting feedback from native speakers on your pronunciation. I'm on a university campus that has an English language school for foreigners associated with it, so I encounter numerous Chinese people nearly every day, in my daily life here. But if you don't, then try connecting with language partners online.
Once you get to the point where your pronunciation is good enough that you are understood accurately like 99%+ of the time when you read words out loud to native speakers, and when you can accurately write down the Pinyin (and tone) for a word when a native speaker speaks it clearly and slowly, then you're ready to proceed.
I found that when I was at this point, the reverse course was actually pretty straightforward. The input method I use, like a keyboard layout but more involved, allows me to type in pinyin and then select characters from a popup. You won't learn how to properly draw the characters, but if typing and reading is all you want, it's fine for that.
I have found that the lack of grammar lessons is actually an asset rather than a hindrance. My experience is that a lot of language learners get stuck in the "book learning" aspects of grammar but can't actually hold a conversation. With the reverse course, you're learning more like a child...you're thrown in, surrounded by the language, and forced to figure it out on your own.
People have told me that Japanese grammar is devilishly hard, and it is certainly radically different from English, but I've found that taking the reverse course is teaching it me much more thoroughly and easily than any straightforward lesson scheme ever has taught me anything. I am quickly surpassing the abilities of people with a year or more of classroom instruction, after only a few months of study.
Chinese grammar is much easier, at least to me, it seems much easier.
If you want an extra boost, between learning the pronunciation and starting the reverse course, there are two excellent smartphone apps: Hello Chinese (my favorite) and Chinese Skill (a very similar one that is also good). I started both before I started the reverse course, and I completed about 2/3rds of Hello Chinese before starting the reverse course.
As a final note, I'm surprised at the negativity towards DuoLingo in this thread. I've found DuoLingo immensely helpful, and for me, it was much more useful than classroom learning. I studied German and Spanish in school, a few years of German, then went to Germany. Later when I went back and started doing Spanish on DuoLingo, I found that after a couple months, I had learned more than I ever did in school. It translated to real-world ability too. I found myself understanding conversations in public, between native Spanish speakers, much more easily after doing only a few months of DuoLingo (before anywhere near completing the course).
Maybe different people learn best in different ways? Or maybe I just know how to get a lot out of a tool like DuoLingo? But I personally have found it the single most useful resource. The only caveat is that with the reverse course in Chinese (or Japanese) you need to rely on a lot of external tools to get you started. In Chinese in particular, the pronunciation is a beast, so I'd budget much more time than you expect, and be patient with yourself...and make sure to check your pronunciation with native speakers to ensure you're doing it correctly! That's the missing piece of the puzzle when most English speakers try to learn Chinese.
Good luck, whatever path you take!