Screw on wide angle adapters any good

[caaaallum]

I've been having a look at these things and was wondering if they're any good. Obviously the more stuff you put in front of the lens the worse the image quality is going to be. However, i have one of these for my LX-3 and it works a charm.

So i thought i'd tap the collective TP knowledge and see what you thought.

something like this ...

http://www.amazon.co.uk/18-200mm-24-120mm-28-135mm-Panasonic-DVX100AE/dp/B002ZYARBQ