Most people have covered the main points, I think. The HPWC is UL listed as EV supply equipment, and the J1772 adapter is listed as an electric vehicle plug/receptacle/couplers. The UMC is not listed, although we don't know why -- it could be that the appropriate UL standards aren't defined, we just don't know. Having it listed just means it was tested by a lab to meet certain specs in the category it is listed. I could probably get the UMC listed as a "safety power unit", but that doesn't really mean much. While I have some concerns about the adapters used on the UMC, it seems like Tesla has addressed those with the new rev of adapters (I have yet to hear of a failed / melted new adapter or charging cut-offs / problems using the new adapters).
Personally, I like the construction of the wall connector much better than the UMC, but I can't quantify the safety aspects of it. The biggest issue for me was having a single UMC and needing to wrap it up any time I knew I'd need it on the road. That could easily be solved by purchasing a second UMC, though.