I like chain guards. I have one on my 520. My other bike doesn't have one and it irks me. A chain guard keeps my socks clean. I'm all over form rather than fashion though. The Shimano ones are bulky looking. Weight to me, has never been an issue. I ride steel frames. I don't race. I need to find one for my other bike with an FSA crankset. I don't want to replace the whole crankset....yet.
"Things look different from the seat of a bike carrying a sleeping bag with a cold beer tucked inside." ~Jim Malusa
2009 Trek 520-Brooks B-17 Special in Antique Brown
2010 Surly Long Haul Trucker-Brooks B-17 Standard in Black
1983 Fuji Espree Single Speed-Brooks B17 British Racing Green