There are reports that some people have had success with cleaning bath tubs using Easy-Off fume free oven cleaner. There are many different types of bathtubs. If you try this, be sure that you test the Easy-Off on a small and inconspicuous area first to see how the Easy-Off will affect the tub surface. Even if it works on the tub, be sure that you also test it on the fixtures. It may harm the chrome or brushed aluminum metal fixtures. You would also need to ventilate the bathroom thoroughly when using this type of product. Keep in mind that it may deteriorate caulking and/or tile grout.
My personal advice is that you should look for a bathroom cleaner that is specifically designed for tubs that will not harm the metal fixtures or tile. There are plenty of cleaners available that should work as well as Easy-Off in cleaning a bathtub without the potential side affects.