I bought one of these to allow me to take low level, wide angle landscape shots. To use it on a Nikon D300 you need to slide off the D300's rubber eyepiece (pretty easy) then slide on the angle viewfinder. It comes with several different adapters to suit various cameras. They are all rather flimsy looking plastic mouldings, and frighteningly easy to lose, but I think tough enough not to snap easily. It attaches usably, but it is far from the firm attachment you might get with a metal clip. Once on the camera, you have a choice of two magnifications. One is 1x and the other is a magnified 2x. The annoying thing is that when switching magnifications, you need to re-focus the eyepiece. This makes it a little tedious, as you may want to use 1x to frame the shot them 2x to accurately focus manually (e.g. for macro work). Visibility through the eyepiece is bright and clear, but best in the central portion (which is what you need, to be honest). The eyepiece can be rotated through 360 degrees, so you can view from any angle, and the image is magically always the right way up. Construction is surprisingly sturdy. It is made from metal and plastic and contains real glass elements. It is screwed rather than glued, and the finish is to a comparatively good standard. This is not junk by any means. It does offer very good value for the money you're paying. The Nikon unit is very considerably more expensive - about 3-4x more. Cleaning the glass in the eyepiece and at the camera end is a little fiddly, but can be done, and there are no expensive coatings to worry about. If you plan to use it occasionally to get the odd interesting shot, I'm sure you will find it a useful accessory. If you want something you can use on a daily basis, then I believe you will be better off getting the Nikon unit. Note that I have only used this on a (DX) Nikon D300. I have no idea whether it would suit the larger FX viewfinder on a (FX) D700 or D3.