Using add-on telephoto lens with A7xx or Gx models

[TexasJo]

Has anyone used the telephoto accessory lens that's available for the A7xx or the Gx? If so, what do you like about it? Dislike? Is it heavy? Does it make crisp images?
I have in mind buying the A710 IS, or the new
G7 (when available) and an add-on telephoto, if I hear from you all that they are worth fooling with. So please give me your feedback.

I have a 3-yr-old PowerShot G3 which is great for everyday use, but I hanker for more zoom ability, and it's showing wear and tear. I also have a nice Canon 35mm with a 70-300 mm telephoto which I've used for wildlife shots, but want to go totally digital.
I know I could try the new Rebel XTi, but it's too heavy.
I'm 69 and heavy cameras like my 35mm give me a back-ache! So I only use them when I'm not hiking far. I want a new rig that would let me leave the film camera at home.
Thanks.

[BowerR64]

The S3 has a 36-436mm lens and is macro and super macro capable. the numbers 36-436 is the 35mm equivalent so if you figure that.

It is a little bigger then the A710 but it has alot more posibilities

[TexasJo]

I had rejected cameras without optical viewfinders. But I'll take a look at the S3 IS. Thanks.
I'd still like feedback on users' experiences with conversion/add-on telephoto lenses in the GX and other Canon point-and-shoot models.

[BowerR64]

But the S2 and S3 has an LCD in a viewfinder so its actualy very consistant. The viewfinder blocks the light so it works well outdoors.