Canon EF 1.4x

Anyone using one? Can you give me the good, bad and ugly with it, please?
I'm really interested in the results combined with the 70-200 2.8 since that's what I plan on using it with.

I think you lose a stop or two.

1.4x = one stop
2.0x = two stops

It worked great with my 70-200 f2.8. I rented one for the Spring Ride last year and it performed as I would expect it to. With the 1.4x your f2.8 becomes an f4, but I believe the camera accounts for this automatically (it would read f4 as lowest f-stop and not f2.8). I didn't shoot any side-by-side shots with it off and on, but I'm sure there are some out there on the internet. I haven't exactly compared the image quality of my shots taken with the extender on and without it, but I do have to say that at first glance, they all look the same. I don't remember any additional "hunting" on the lenses part to find focus, either.

http://www.the-digital-picture.com/Reviews/Sample-Pictures.aspx?Equipment=112&desc=Canon-EF-1.4x-II-Extender-Sample-Pictures

I've currently got both the Canon 1.4 and a Kenko 300 Pro 1.4X, I've actually stacked them on my 400 f5.6L because the cam still AF's (2nd TC doesn't report) and the IQ is better then a 2X by itself. The advantage of the Canon over the Kenko is slightly better color and better build quality and it's white so it matches your L teles. Canon disadvantages over the Kenko: more expensive, larger-heavier, and won't work with all lens because the canon has a protruding rear flange.

Sharpness is a draw AFAIC based on a bunch of tests I did with both on a 300 f2.8L IS. Both TC's report to the body so as Walt/Scott pointed out you lose 1 stop automatically. Tamron makes a cheaper version that actually doesn't report so your 70-200 f2.8 will still be an f2.8 (at the expense of some sharpness as it's just not built as good). If you are planning on using it a lot and want to squeeze every drop of quality possible get the Canon, if not save some money and get the Kenko because it's 98% of the Canon IQ wise.

A couple of examples with the Canon 1.4: the bird with it on my 70-200 f4 IS and the the DB shot with it on the 400 both shot handheld.

Awesome! Thank you...