IMO,
Pro- Less Friction,Longer Barrel Life,and generaly Lower Muzzle Velocity for the same load,although in a couple of mine it went up slightly.Reduces cooper or lead fouling.
Con- A little messy to do yourself but can be done,messy to load,A pain at times to load as the bullets are slick,and can be a pain to remove it from a barrel as it will inbed (for lack of a better word at present) itself to the metal.
I feel the best use of it is for Target Shooters or Varmint Hunters where a lot of rounds will be fired.I also think it can change the way some barrels behave after cleaning,but haven't used it enough yet to prove it.Have read some reports form others who feel the same.