If you're in the United States, the rule states that no one is allowed to buy and import lasers above >5mW (that is, Class 3B and Class 4).
To burn items, you need around 100mW and above, which is clearly >5mW.
From these two facts, there can be two outcomes:
1. Either they're falsely advertising, which in this case you shouldn't buy them since it is a scam, or
2. They are telling you that it's actually higher power, but under-declaring it by putting it as 5mW so that they can bypass the regulations and sell to the United States.
In order to know which is which, you'll probably have to research a bit more.