"A cheap copy of a professional tool that performs almost as good as no tool at all! Don't waste your money on this.
The straight top half is about 2mm offset from the curved bottom half so it fails to wrap around the pipe properly and initial pressure on the handles crushes the pipe between the two offset halfs so the bends end up with a 2mm "seam" all the way round and almost completely blocked internally.
Spend more and get something that has been made properly. Screwfix shouldn't stock this rubbish."