All bleaching is temporary
Most sensitivity from whitening is from dehydration during the process, and goes away in 24 hours. Some Ibuprofen in advance can prevent extreme pain, but discomfort is common.
While Zoom is a single visit process, the effects are hit or miss. Some people are happy, some not. Effectiveness is truly dependant on dose, duration and frequency. Dose would be concentrations of gel, duration would be how long the teeth were exposed (all night long? 2 hours per day?) and frequency would be...