There are 2 Convoy UV models, the S2+ UV which uses a Nichia led and doesn’t include the UV filter and the newer S2 UV without + which uses a LG led and includes the UV filter as the LG led creates more visible light. The S2 model has higher output and it’s floodier while the S2+ has a higher intensity.
Because the US patent office granted a patent to somebody for UV flashlights with a filter which shouldn’t have ever been granted (as it isn’t a novel idea) , the S2 UV without the + cannot be shipped to the US. However if you are in the US you can still buy the S2+ version and buy the ZWB2 filter yourself.
Edit: I don’t support such patent abuse (I don’t live in the US anyway) but here is the link to a commercial site explaining the situation
http ://www.fluorescents.com/products-uv-flashlights.html
The site sells the S2 version for higher than the original price (2x18650 and a charger are included to be fair but that doesn’t make up for the price difference). Perhaps some of the price difference would go to Simon (Convoy’s owner), but I guess most of it would go to the site and to the patent owner.
Edit 2: This thread has more information