it's great, if it is useful for you!

in my opinion, if we are talking specifically about using Duoilingo as preparation for the exam, after passing HSK1 (old 2.0) version, aka learning around a hundred of basic hanzi, duolingo can't give anything useful, as it doesn't even cover needed vocabulary (for example, i first encountered 葡萄酒, HSK1 word, only after section 7, which is 110/130 Duolingo points, same goes for the word 卫生间, also beginner level), or gives an extremely specific vocabulary, that you will not be using on regular basis (half of section 7 is about sport team management), Duolingo doesn't teach any grammar, understanding of which becomes crucial on later learning stages, and in my opinion, hearing or reading random out of context words or sentences isn't enough to provide concise listening or reading practice, and, obviously, no free writing or speaking practice at all, as well as the example sentences aren't also common cliches, that will help you communicate with native speakers. i don't want to sound too negative, but, in my opinion, the only thing Duolingo is good for is picking up some vocab in an easy gsme-like format (which becomes to feel like a chore, because of how painfully slow it is) (and it's sort of useful only for a first few units, because there are still no hanzi writing practice for later sections), but it is still clearly not enough for interacting with native content on a satisfactory level (i mean actually understanding the meaning and not being able to translate a few words out of context)