I Bought one of these.
The voltages they quote are not regulated. As the battery runs down the voltages all drop. near the end you have something like 3.3, 2.7, 2.3 V.
Somewhere in the middle you might have 3.7, 3.2, 2.8.
The higher voltage is about what a Riva puts out, for about 1/2 the price.
The don't tell you this, of course. Bet you thought you'd get 4.2 V until the battery ran down, didn't you ?
I also tugged on the battery the wrong way and it came apart and broke both wires
inside. Couldn't figure out how to fix it, so it went into the trash.