Was thinking of getting a folding tang sight for my 1873 Uberti....several questions:
1.  Do you have to remove the open sights?
2.  Does it "co-witness"?
3.  Adjustable for windage and elevation?
Thanks....

I like tang sights.

You don't have to remove the rear sight but you'll never get the full potential of the tang with the rear blade in the way.

I just put a Lyman on my Rossi 92.  I had to drill and tap the tang for the second screw but it was easy.

I am trying to fit a folding rear blade as well but it's a work in progress.

The Lyman isn't windage adjustable, you shim the sight left or right then drift the front to do finalize.

I cowitness to get a sight in then either fold the sight down if I can or remove it.

I like tang sights alot

I've got tangs on mine.  One of them has a fold down as well; the others have the regular sight removed.  FWIW, I never use the fold down sight on that one rifle.

They're all adjustable for elevation.  Usually not adjustable for windage, but you can shim one side or the other if you need to center up right and left.

http://www.marblearms.com/products.html