One has a 1x-2x magnification and the other has a 1.25x-2.5x magnifications, and just by looking at the photos the 1.25x-2.5x viewfinder has a metal mount, where the other has a plastic mount. Depending on your planned use, those things may make the difference for you. If you are going to be manually focusing with one of these, the one with a higher magnification may be the better choice.

To answer Jeff's question about the need for one of these, I can say this. Up until I got a camera that offered a live view LCD screen, I was in the market for one of these. The right angle view finder would have come in very handy for shooting things very close to the ground. It's not easy to get your eye to the view finder when your camera is sitting on the ground. Now that most DSLR's offer live view, I no longer see the need for something like this in my kit.