With my limited education in pursuing trout first I like metal beads because I hate split shot, but I like glass beads for the air bubble appearance they give.
But the bigger question to me is, why change a fly because its appearance has become unkempt? Some fishing lures of all sizes, from flies to crankbaits, seem to have a certain hard to discern quality that makes them catch fish. Sometimes the more battered they are, the better they seem to work.
"Patriotism supporting your country all of the time and and your government when it deserves it"- Mark Twain