Here it was so clear that this lens is a piece of crap that I combined the quality with the range to emphisize a point.
The TOP is my sony dsc-f717 with its 10x zoom (2x digital-5x optical).
On the bottom is my camera with 5x optical and the "2x" telephoto lens I bought.
As you can see there is about 70% degredation of the photo quality especially around the edges. It is also not a true 2x telephoto lens. I estimate it is probably around a 1.4 and that may be generous.