Not good, unless you intend on selling your vehicle in a short period of time. I generally buy a 60 or 80,000 mile tire in a good brand name. Safety on the road is your main concern and cheap tires should not be on your vehicle. Watch out for tire sales, especially before Christmas when people are spending money on presents and not tires. The tire dealers know this, especilly PepBoys, if you have one near you.

Not good at all. Cheap passenger car tires should get at least 35,000 miles.

You've answered your own question. Just remember, you get what you pay for, e.g., my last set of 4 cost me $800.

Very good? Whatever...

Tire tread life is dependent upon three things: 1) The construction of the tire 2) The condition and adjustment of the vehicle suspension. 3) The driving style/habits of the owner. High performance tires are constructed of softer rubber that improves handling and braking, but sacrifices tread life (e.g. race tires last only 100-200 miles). Whatever the qualities of the tire, if they are mounted to a car with worn suspension or improper alignment, the tires will scuff and drag on the pavement. This makes tires wear more quickly. If you are an aggressive driver that accelerates quickly, brakes hard, and screeches the tires around every corner, your tires will wear out much faster than someone with a conservative driving style. That being said, 20,000 miles is rather poor mileage for passenger car tires. Generally, only very high performance cars have tires that will wear out so soon. If you need advice on how to select the proper tires for your car, Tire Rack has excellent material that is freely accessible. http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=31 If you give us more information about your vehicle, your tires, and your driving habits in the comments section, we can advise you further. Good luck.

Explanation of tread wear, durability, etc.: https://www.kaltire.com/utqg-ratings/