There are several reviews that are quite negative, but I think most of this can be resolved with two simple tips:
1. These are quite a firm fit, care should be taken when fitting / removing from body / lens. A VERY small amount of light oil helps tremendously.
2. To use with lenses that do not have a manual focus or aperture (the standard Olympus ones don't) first attach lens to camera, then manually set the aperture you want, and focus to closes distance. Now remove lens, and it will stay with these settings. Now fit the extension tubes and physically move the camera or adjust the zoom (if a zoom lens) to focus. It takes some trial and error to get the lens set-up correctly, but it is possible.
If working within these limitations is not desirable, then you need to spend more money on the tubes that connect the power from the body to the lens, but for the price these limitations are well worth living with. It is possible to get some extremely close-up photo's with the 42-150mm lens. The 14-42mm lens is not so good, but can get some good results.
Overall 5* because you can get decent macro photo's with these extension tubes with an E620, which for the price is excellent value for money.