First here is the good news.
Optically the product appears to be good and works well as a 3D viewer once things have been set up properly. It is light weight and can be folded flat for carrying indeed it comes flat packed from the manufacturers. This makes it easy to take along to friends to impress them with your 3D photographic skills.
Now here is the bad news.
Overall the viewer is flimsy and the plastic mounting frame with its clip together mechanism can easily become distorted making it a bit fiddly to properly align the prints for viewing. There are no instructions on how to set up your stereo pairs for the best effect so it took some experimentation to get the correct photo size and spacing - I use pairs of prints that are 60mm wide printed side by side allowing me to print 2 sets of stereo pairs on one piece of 15 X 10 cm (6in X 4in) piece of photo paper. These prints are quite small and a viewer using larger prints positioned further away might be better. The technique of placing the prints on a horizontal plane, laying the viewer over them and viewing them vertically from above is also not ideal and there are other hand held viewers that hold the photos in place so that they can be viewed at a more comfortable angle which may be better, although these tend to be old and difficult to acquire.
Overall this equipment does the job. It was a bit expensive at its original price but at the reduced price I paid it was reasonable. value