I used to have one of these, and it wasn't so bad (with the usual mirror lens issues--fixed aperture and "donut" out of focus highlights and double-line bokeh, but on the upside, mirror lenses are inherently apochromatic). The main attraction is how compact it is and an easy way to carry a 500mm in your bag. I only sold mine when I got a 600/4.5 refracting lens. At $49, this is a fantastic deal, if you don't happen to have a long tele.
It still requires a tripod, in my opinion, even though it is handholdable in terms of weight and size. I think this is where mirror lenses get their bad rap--they're so easy to carry, users forget that with such a narrow angle of view, there's no real way to hold it steady below 1/2000 sec or so, and at f:8 that means using a film with a speed of EI 1000 in full sun.