uPVC window industry has many inexperienced players. They use multiple profiles and most of them are cheap. poor quality windows fade after a few years.
Hence double-check their brand, ask from where they buy etc., before placing your order.
In some cases, low-quality hardware will be used, which will give trouble after a few months of usage. When the hardware is not functioning properly, this will leave the customer unable to lock the window properly and hence water will begin to come inside. Ultimately it will result in customer displeasure. check the hardware properly.