Are these lenses worth buying?

I was checking lenses and found out this one. They are cheap so I don't know if it would be worth buying them. I have a 55-300mm lens and would like to get more zoom without losing quality in the picture. So I was thinking if these lenses are good or not. And what would ypo recommend.

Thank you! =]

Rokinon 650-2600mm
http://www.ebay.com/...0679791626

6000mm
http://www.ebay.com/...0983247360

Rokinon 500mm/1000mm
http://www.ebay.com/...0543645342

Price tells you everything. These are not quality products. These kinds of lens would cost you a couple thousand dollars each, and more.

These are preset lenses - the 500mm isn't a bad performer, but I'd think twice about using the teleconverter.

There are no elecromechanical contacts between camera body and lens, so you'll lose autofocus and most, if not all, of your metering modes. Even if metering is permitted, it's stop-down only.

I use a 400mm f6.3 on my Canon (I've had it for years) where it allows stop-down Av and M metering, but its little eccentricities take a bit of getting used to.

Two are Nikon mount and one is for Canon. Get only if it will mount your camera. At that price, expect picture quality to go as close to trash as possible.