FYI - Evidence suggests men's genitals are the one area where UVB is associated with cancer risk.

Personally, I've been burned by cheap Amazon devices. Literally. I started with one of these https://www.amazon.com/dp/B07P6GP64V/ and it was terrible

1. Counterfeit "Phillip's" bulb
2. Definitely not FDA approved
3. Low-quality UVA/UVB output (not narrow-band UVB, unknown spectrum distribution)
4. Inconsistent output, UV intensity rapidly faded over 3 minutes. Turning the device on and off to treat more than area would lead to guessing intensity, and inevitably UV burns
5. short bulb lifespan (3 weeks - might have been low-quality wiring)

imo that was a stupid gamble. True nbUVB is (mostly) safe within treatment protocols... but it's very hard to make sure that's what you're getting, nvUVB is invisible and you don't want to treat yourself with UVA by accident (especially with topical steroids/immunosuppressants)

Proper nvUVB devices are expensive because they are calibrated, certified, and tightly quality controlled medical devices. The market simply isn't big enough to support cheap and high-quality manufacturing.