A minimum of three or four times. Often more. I have reviewed products I've had for years.
The first use of a toy, you are learning how to use it and are not getting the full spectrum of enjoyment from it, as you're learning the buttons and speeds and patterns (if it's a toy) or if it's a cosmetic item, it may take more than one use to see if it really softens or if you are sensitive to it. I like to use lube a number of times, in several different ways, toys, anal, sometimes PIV, digital play to see how it performs, if it washes away nicely, if it's sticky, if it moisturizes, if it irritates me etc. You would not be able to do all that in one use. Some irritations only show up after several uses or several days of use.