This is not a watered-down "demo mode." During these 14 days, you get access to the of Tableau Desktop, which is normally priced at $70 per user per month (or $840 annually). You can:
Tableau Public is excellent for building a portfolio, learning the software, or visualizing open data. It is for business or sensitive data. how long is tableau free trial
If you don’t need to keep your data private, is completely free forever. However, it has major limitations: This is not a watered-down "demo mode