I have 3 sets of these curtain rails and they have been running flawlessly for several years. The build quality is excellent. One set from a different supplier was quite long and cut into 3 sections for shipping. This is less ideal as the runners have to pass over the join, so worth avoiding if possible.
I helped a neighbour fit the same rails into his bay window. We did disassemble them to adjust the length but it isn’t a simple procedure and I would recommend accurate measurement and get the supplier to cut them to size. Also, the 90 degree brackets supplied were made of plastic, so not as robust as the metal straight sections and the runners don’t go round them as smoothly. That said, his have been working for over a year so far.