Materials aren't the issue with the cheap 510 extensions. They appear to be made out of mild steel and plated similar to the expensive ones, but I'm not positive about that on either part. In any case, the metal is harder than the brass press-fit connectors for both parts. The more expensive of the two parts is highly solderable, but I haven't tested the cheap ones for solderability. The main problem with the cheapies I've found is the poor tolerance on the threads, mainly the female atomizer connector. The male side seems to be okay and should provide any support you need. Also, the center post on the cheapies is some wierd looking thing I've never seen before. The center post on the expensive ones is similar to the center post on the brass press-fit ones.