Tbh who doesn't have a phone and the usb dongle is a lot smaller than a device with a battery included.
Kids who go to summer camp where they (thankfully) aren't allowed to use phones are a great market for mosquito itch reduction devices.
I did look at that. Seems to be about the same price as the USB one in the UK. But it also doesn't recharge nor does it have fine-grained controls for session length / intensity.