>>4387835They're light, but bulky. You can get monocular ones that are smaller, but the Sinar is rare and about 3x the price. Cloths suck compare to a binocular reflex viewer, and it puts your image right side up.
The other goofy less good option is to use a bellows instead of a cloth if your camera allows it. I carry a spare bellows or two to use as a compendium lens hood anyways...