Its definitely a plus factor if the product is ready but I would not rule out a good ICO just because it does not have a product yet.
If the product, whitepaper and team are good, and if the roadmap is being followed, I see no reason to exclude an ICO simply because it does not have a final product yet. An example of such a case is DIW Token who did not start off with a product but have succeeded in realeasing the alpha version of their product 2 days before the end of the ICO