I received two Chinese batteries and a wall (+ USB output) charger from Hong Kong for $12.

The wall charger supplies a very stable 4.2V to the battery and has an auto-off circuit to prevent overcharge. No clue if either the charger or battery has a more intelligent controller (usually required for safe operation of Li-Poly packs) and I'm not tearing them apart to find out.

USB output is similarly stable 5.0V.

I'm going to use these while keeping a careful eye on them. Statistically speaking, the risk of fire or explosion is vanishingly small, so I'm not going to be losing any sleep over this.

Overall, looks to be good quality construction for very inexpensive price.