Tung oil really amounts to a type of varnish (cured rather than evaporated setting process) and has some of the same advantages and drawbacks. It will be better against water and might be tougher than shellac. OTOH, shellac is reparable - new shellac will meld with the existing finish very well - whereas with cured finishes repairs will be separate from the original finish (less any mechanical connection from roughening.) You also don't have to worry about the cloths you use for shellac catching fire on their own
