Tricky-If waiting is not an issue thats fine. Or if you already have the non adjustable stock and dont want to go through the hassle of selling it and getting an adjustable one, or if you change scope and now your non adjustable stock doesnt fit... You get the idea.
When someone is starting a build I advise guys to go with a new adjustable stock. Sometimes the lead times are very long and its easier to get a non adjustable and have it retrofitted. Cost wise it is about the same, sometimes cheaper. And theres some stocks that are not available with adjustable cheek from the factory. So its just another option out there.