Hello all, I'm new here and just saw this thread and thought I'd chime in. I own two of these locks. I have a black one and a white one. I ordered mine from Amazon and they shipped from China in a small, white plastic bag that actually said "bondage lock" on the outside. I was somewhat mortified but I'm friends with the mail carrier and to be honest, I don't think he noticed.
As far as the locks go, I can't speak for all locks, but in my case the black one seems to have different firmware than the white one and thus, I feel like the black one is of a higher revision. The difference is that I can silence the black one by holding in one of the buttons for 5 seconds whereas the white one does not seem to have the same function. Also in my case, the Li-on battery in the white one is not in great shape even when I first got it. It doesn't hold a charge for long. The black one has remained locked on me and counting for at least 14 hours. As for safety, they both have a reset contact. If you use your finger nail, you can pry up the plastic display cover exposing the two screws. Look inside the hole under the left screw. You will see interlaced traces on the circuit board indicating a contact spot. If you stick something metal in there and short it out, it will reset to the default state of no countdown. If it's locked when you reset it, simply set it for 1 minute and wait for it to unlock. If you're battery runs low when you're using it, you should be able to just plug it into a usb and reset it as I've stated. At worst, you may need to keep it on the charger for a few minutes before resetting.
My advice according to my own experience; if you're going to buy these locks, only buy the black ones. I've seen them on aliexpress for decently cheap and on wish.com for $11 plus shipping. They're pretty good, especially if you like locking yourself into a PVC lolita maid dress and doing chores in the house. ^^
