I'll pop in on this thread, just for the record.
Several years ago, I purhased the Z-tek catalytic converters, y-pipe, mid pipe, and muffler.
The catalytic converters were the first part to go. The welds opened up around the bulging portion of the catalytic converter, so I removed these and threw some test pipes in to get by.
Next, the welds where the three pipes come together on the y-pipe started to break apart. This happened so quickly that the whole y-pipe came apart at that junction. I have since replaced this y-pipe with the Kakumei with no problems (at least 2 years ago).
As far as the mid pipe and exhaust go, they have not fallen apart yet, but I wouldn't hesitate to get rid of them if the right opportunity arose. I'm also really glad I didn't go with their headers, I bet those would have lasted less than 6 months.
I did also e-mail Ztek about getting these replaced, but never heard back. In the long run, I would not have put these back on my car even if they had sent me replacements.
This is roughly the same story with the Megan products - I just took off a warped set of headers last weekend, and the test pipes I had were a joke (O2 sensor bungs actually fell off).
