Great idea and very useful when set up properly. My main complaint is that even with the extender firmly attached to the flash, it can be very difficult to line up the flash evenly, since the weight of the extender tilts the flash down a few degrees, which means flash coverage area and field of view on your telephoto lens are not aligned. I use a Sigma Sport 150-600 lens. I've had good results with the product, but it's still a work in progress.