it doesn't guarantee for the ICO that have a working product can get success after they pass every phase on the roadmaps. They still need to work hard to get more investor or buyer to buy their product, and it's not easy to do. Besides that, they should compete with the other ICO that might have a similar product
This is the reason why we must choose and contribute to the ICO which is having unique products/solutions so that they might be having better chances to become successful and their token will sustain with better price levels. Competitions is everywhere still how heavy their promotion will bring the differences.
I think investing in a working project is profitable and it will be a long run investment but its better to look deeper in the projects goal and how it works and then you can judge if its really worth investing
Working project might be just an eligibility criteria for choosing an ICO but it will never guarantee that we can make profits with that ICO. Moreover, many scam devs had just showed some working model and then stayed inactive which ended up investors go losing all their money. This is the reason, even with a working model, ICO investments are still just a gambling as it has only less than 50% chances for better ROI.