Since your not getting any other replies I'll try to give some advice. I have not used the 550 nor either of those auxiliary lenses; I'm a Kodak Z612/Schnieder 1.4x owner.
First, remember the 550's 18x lens is a very complex extended zoom lens to begin with and as a general rule the more complex the lens the lesssatisfactory the image quality with any kind of add on lens. The greater the zoom range of the lens the more difficult to adequately correct aberrationsfor the entire range of the zoom so there's little room for adding another set of aberrations with an aux lens.
The Olympus 1.7 TCON is held in high regard among Kodak superzoom users and Kodak, on P Series cameras which require a setting change with auxiliary lenses have a specific setting for the Olympus. On the other hand Tokinas' only reputation is cheap.
There are a number of auxiliary lens comparisons available (including the 1.7 Oly and the3x Tokina) at this site:
http://www.cs.mtu.edu/~shene/DigiCam...-30/index.html. The Panasonics FZ30 was the test bed. That reviewer was of the opinion, base on his tests, that the Nikon 1.7 was the best but was very costly. Among the more rationally priced the Oly and the Pany were very good.
I'd suggest notbuying a TCON at all but if you feel you must then stick with the Oly.
Remember, the winner is not the one with the most toys but the one with the best results.
