NextDoc does great designs and is good at responding to directions. I have only used it to develop 2 long documents, which consumed all my credits. The issue is that it can undo past edits when doing new ones. And simple things like updating page numbers can take over 20 minutes (it will do it in batches of 4 or 5 pages). Plus, when it makes a mistake (and it will admit it missed content etc), but will still charge you credits for its mistakes.
It took me almost 4 days full time for these 2 documents. I would have appreciated it being quicker. The end product is great though. So you need a lot of patience, and an acceptance your credits will vanish if your documents are longer than 30 pages. I havent tried any other type of document, as this is what I needed to get done as a priority for a client. I wont be refunding, but I also will be investigating my Canva subscription more closely to see if it can do the same thing, and if it is more intuitive about the basics like margins and page numbers.