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It uses peltier effect, which isn't very efficient. There are more efficient ways. Also, personal peltier coolers are really old tech. The article says Sony incorporated their cell phone heat dissipation technology, which means patents. But overall it seems like good product design with mediocre tech.

Using it outdoors probably isn't too bad. It can remove heat faster than skin can conduct heat from the air, and faster than sweat. It can also help during all these wet bulb weather events that are increasingly common.

As far as battery usage, I can't find anything on capacity. They say 100 minutes charge, commenters say it lasts about 2 hours on full charge. Given the size it's probably similar to a cell phone battery. A blurry image I found looks like it says 1.5 amp charging rate. This would put energy usage at around 5 watts with a smaller than average cell phone capacity. According to physics Substack, people generate around 3 watts of heat at rest. So it is just powerful enough to cool you. Also why it says only "light exercise" in the ad copy presumably.

As for energy efficiency, it's actually probably very environmentally sound. But it has lithium ion batteries, plastic, integrated circuits etc. So in that sense, not so great.

Also it's best use case is for riding mass transit to work. Working from home would be so much more environmentally sound.