Ciderspy,
normally, we are not that cranky 
It's just that we find it hard to believe that somebody who wants to spend something like 200$ on an upgrade for his camera would not appreciate the possibility to educate him/herself as thoroughly as possible rather than just take the first opinion voiced.
If you read the threads, you will realize that
- the Canon teleconverters are very good quality (for a price)
- The Olympus teleconverters are also very good quality (for a maybe slightly cheaper price ... but you can get these at *very good* prices at the ebay seller mentioned in the tread I pointed out)
- The Kenko KNT-20 (LD20T) is also very good quality at an affordable price
- The Kenko KUT 300 has not been tested by anybody yet ... it might be good, but it might not be. Still, it's twice the magnification, so I would be a bit wary
- Vignetting can always be an issue with teleconverters, so pay attention that the rear thread size is not too small (there are 58 mm, 52 mm, 43 mm and 27 mm filters, the 27 mm filters might give you problems here)
- stay away from eBay offers of Opteka, Crystal optics and Merkury optics.
Hope that helps 
Best regards,
Andy