What is the 365nm UV mode good for?

It makes fluorescent materials glow: security marks on currency and documents, UV dyes and leak tracers, and some cured adhesives. It works best in a dark room, since daylight washes out the effect.

Through the USB connector using the included rechargeable battery. A standard USB-C cable and charger are all you need; no separate battery charger is required.

Is it actually waterproof?

It is rated waterproof, so rain and splashes are fine. Avoid pressing the button or opening the charging port underwater, and do not dive with it.

How does it compare with a plain 1100-lumen pocket light?

You give up nothing on the white beam and gain the UV emitter. The trade-off is a simpler interface and no zoom, so rivals with adjustable focus are more flexible for long-range use.

People who want one small light for daily tasks plus UV inspection, such as technicians, hobbyists and homeowners checking leaks or marks. Casual users who only need a white beam may not use the UV mode.