I have a pair of the polarized sunglasses with the magnifiers in them.
They are great for tying small flies on, and really aren't in the way when fishing.
Like the bifocals, you will have to learn to look a little farther down to see where you are stepping. I didn't have any problems getting used to them.
One thing to note. Down here, we only have sand bottom streams to fish, so I haven't had to worry about watching for rocks.

Kirk

PS. I've since had to start wearing progressive lenses for everyday. I got a pair of the clip on, polarized sunglasses to fish with. I haven't used the others since. I only needed the others to tie on a fly, and I can do that with the precsription lenses.

kb