There are really bad quality T12 tips, with too much resistance in the internal wires.
I had a tip that melted at the top, not the connection, but the nylon between the steel tube and the internals.
The whole tip was burning as hell.
After dissection, I could messure about 2ohms in the wires going to the heater!
Other tips are better.
I guess original Hakko will be much better (and expensive), but hey for $3 it's a nice deal.
Now that the JBC tips are starting to grow in the China market, I hope to see some cheap quality copies coming soon.
I'm waiting for a few I bought 2 months ago, they looked great at only €6.