Recently comparing Duolingo to Hello chinese app to learn mandarin as a 汉语 learner newbie. I would say Duolingo is good for you to learn new vocabs and train your muscle memories in writing hanzi. Hello chinese is whole new different level, it teaches grammar pretty fast and can make beginner without basic proper hanzi understanding feels overwhelmed by the grammar. Hence I would recommend to use both, but Duolingo first, at least chapter 1 and 2, then you try 1st chapter of Hello Chinese.