Supremely useful. I've bought 5 of these now.
"It's just the right size and weight to be one of those "I'm so glad I brought this" things -- it's a great flashlight, that's a given, but the power bank feature is a huge bonus for all-day outings. If I had to nitpick, it seems like it doesn't hold its charge quite as well as a dedicated power bank, but if that's the price of versatility, it's worth it."