They are OK for casual riders, that is their main market.
Depends on what you want them for. The good ones do a good job of dealing with road buzz and taking the edge of small hits. But they're not really a valid alternative for a full-suspension bike.
Northrock Bikes, Inc. is a good, reliable US brand. They are sold by Costco.
Yes, you can trail ride a motocross bike, however the stock gearing and suspension on a mx'er aren't the best for trails and woods.
Viking has some good bikes. They make a full range of bicycles. The Milano is "entry level" with it's generic parts and entry level Shimano components.
Usually you don't actually need it, bikes w/o suspension are still more common than bikes with suspension.But you may certainly want it. Suspension flexes and compresses when you ride over a bump - just like on a car or a motorcycle. Good for comfort and traction when you are on bumpy ground, but it steals some power when you're riding on flat surfaces.Only if you are doing big jumps you might actually need it. A suspension bike can take a bigger drop w/o breaking itself or the rider than a rigid bike by soaking up some of the force of the impact in the suspension parts.Then again, it's pushing things to say that someone actually have to ride big drops.
are framed bmx bikes any good
Bicycle stores have good bikes, not department stores.
Fezzari bikes are pretty amazing.
yes
yes
Fezzari bikes are pretty amazing.
I'm having Trouble understanding your question. I'm assuming you mean "why aren't mountain bikes as good as road bikes". Just like different tools are good at different tasks, different bikes are good at different types of riding. MTBs aren't good for road riding b/c the suspension steals pedaling energy, the wide, knobbly tires roll heavier than narrow slicks. The more upright riding posture creates extra air drag. During fast descents they eventually run out of gears. OTOH road bikes aren't good for off-road riding. The narrow tires bog down on soft surfaces. It's Easy to get pinch flats. The ride is harsh.