A teleconverter, or Extender as Canon calls them, is a cheap and convneient fix when you need more reach. Rarely is it the first choice compared to a a longer lens of the same focal length.
They simply magnify the centre of the lens image, inevitably losing light as they do so - one stop for 1.4x and two stops for 2x. This often takes you beyond the threshold for AF to work, usually f/5.6 on crop cameras. In magnifying the image, if the mother lens is not of the highest quality, they just magnify any shortcomings too much. They also don't work well with short focal length lenses, due to the way the light cone hits them, which means 200mm or longer.
A few zooms are good enough to take one, such as Canon L, but they only work decently with long primes, like 300mm f/2.8 for example, or 600mm f/4. Even then, the light loss often rules them out in practise.
Of course, TCs introduce their own optical problems and apart from the Canon and Nikon ones, only the Kenko Pro models have a good reputation. Sigma have a good rep, too. Canon and Nikon TCs also have protruding front elements so they won't actually fit a lot of lenses.
With your lens, frankly the image quality won't be up to much at all. And that is if you can live with the dark viewfinder, a high f/number, and loss of AF.
