They are better than nothing, but do not take the place of binoculars.
My buddy lost an eye in an auto accident a few years ago. Only person I've ever recommended a monocular to, and he chose a Swarovski 8x30 Laserguide. Waste of time otherwise, IMO.
When I needed a new rangfinder I bought a Leica because I fugred with quality glass I wouldn't have to carry my binoculars - WRONG! With only one eye you have no depth perseption and sometimes even finding what you want to look at because of it.
My buddy has poor eye sight on his left eye. We can fit him with different binoculars. None of them works out. He ended up with a pair of 10x42 monocular, which works out great for him.
lt7010,
If you wear glasses you will need at least 13mm of eye relief. I have been checking them all summer. I want them to carry on my belt instead of the compact binos.
I use a Brunton 8x42 for Turkey Season. I find it great for quick scanning of areas and id of birds. Not great for long periods of glassing.
I'm ordering a Minox
http://www.minox.com/index.php?id=3589&L=1For Christmas. Will report more on it then.