I know the AS very well as our system is in the Australian WERS, tested for Australia as well and approved to use there, including bush fire rating !!!! I am very well trained in the technical side of uPVC and thermal expansion is all depending on the chamber design, chamber ventilation, and the uPVC material itself and there a re size limitations but certainly not 1500mm . I have recently made a report for a court case where some Chinese stuff failed in the heat. Our system is successfully used for a very long time in Australia, middle east as well as opposite climate places such as Scandinavia or Siberia.
I take no short cuts and my windows work extremely well and look great and I get comments accordingly.
I know some Australian window manufacturers personally and they do well, and the quality feedback is from my Australian customers and not mine. And I have always pointed that out.
I don't know what reasons you had to withdraw your uPVC system before having a replacement and I don't know what technical issues you may have had, but you should not assume that others have that as well.......
It is a bit like one model or brand of diesel car keeps breaking down and then one comes in a forum and tells everyone that all diesel cars a not good.