Aside from getting toddlers to cooperate, it can also be a great tool for making transitions easier for kids with autism and ADHD. I even use it to help me stay focussed while cleaning if I have a limited amount of time.
The timer can be set for up to an hour and is totally silent until it goes off — no obnoxious ticking noises while you wait. When the time does go off, it's a beeping sound that's loud enough to hear without being startling.