The copper foil technique may or may not have been invented by Tiffany, but he certainly used it extensively in his studio. Thus it is often referred to as the Tiffany method.
It is neither easier nor more difficult than lead. However, it’s significantly cleaner because it does not involve the use of whiting or cement, which is why this technique is most often taught to beginners in North America. In Europe leading is most often taught first.
Some people deduce that copper foil must be stronger than lead because the solder goes all the way around and between each piece, but lead is still the preferred method architecturally, holding up huge weight-bearing windows for hundreds of years.
One thing copper foil can do, though, is allow stained glass panels to curve, as you can see in the multitudes of Tiffany lampshades that are still around today.
There are a few other differences from lead in the construction of copper foil panels. First, copper foil is less forgiving in that there is no channel to hide errors in glass cuts. Precision in cutting becomes especially important.
However, while cutting may be a little more difficult, soldering foiled pieces is a little easier because you can’t burn through copper foil the way you can through lead. If you accidentally apply too much heat, the solder just drips through to other side and forms a ‘mushroom’ that must be cleaned up later. Or it cracks the glass.
Finally, lead panels are usually constructed from the corner out (pieces of wood form an “L” shape and the panel is started in that corner and grows up and out). Copper foil panels are usually started inside a (temporary) wood frame that goes all the way round the panel, like a picture frame. You don’t need to start in one particular spot because the pieces aren’t going to shift within their frame.