- What is it good for?
A lot. Any bodyweight exercise you want to make harder can benefit from a vest. I've used them for pullups, lunges, step ups. I've seen them used for pushups, horizontal rows, sprinting, box jumping, squats, burpees, split-squats, while sled dragging, etc. They're pretty versatile.
- Can I use it just to wear around the house 1 hour a day and expect results?
I suppose it depends on what you do for that hour. Probably not too much overall, but I've never heard of anyone doing it. Give it a shot.
- Will my back suffer as a result?
Also an "I don't know." Not for exercises, certainly, but maybe if you're wearing it around all the time. But if you're doing exercises correctly it's just a convenient way to add resistance.