I bought safetytats for our upcoming trip and decided to test them on myself. I put one on my stomach and went about life. I exercised, took showers - but didn't actually rub soap directly on the tattoo or go swimming in a pool. Anyhow, it was readable for about 5 days.
So I will be using them on my DDs while we are on vacation. I may have to reapply them at some point but it came in a set of 16 so I have plenty, and overall I felt comfortable they would do the trick.
Good luck deciding.