Li-ion is indeed dangerous, but I do not think that third-party batteries are built without the necessary safety circuits.

This is actually the most important problem with counterfeit batteries. Third-party ones bear a brand name, just not the one from Nokia. Even if the manufacturer is in China, they do not really want to be associated with customers going in flames.

Counterfeit goods are illegal, and bear no name (or rather a false name). If they fail, and they do, the manufacturer is nowhere to be found. Besides, for this counterfeit battery, the manufacturer invested great expense to have a counterfeit hologram made and a label quite similar to the original printed. Yet, it costs about the same as a third-party. On what do you think they have saved?

I should say that I have a relatively good experience with third party batteries, and not only for Nokia. You take your luck, some fail (one 1 in 4 or 5 in my limited experience), but mostly they are similar to the original models. When they cost a third of the price or less, I am willing to take the risk. They can even cost a bit more if they are sold under an European brand (which means I have a usable warranty and they will get into real trouble if the battery goes in flames).