VS1 should mean that you shouldnt be able to see it with the naked eye. Additionally if that''s the only inclusion, I think most jewelers can hide that behind the prongs.
As far as whether it weakens the diamond being at the girdle or some other red flag, I have no idea, but I wouldn''t expect it to.
If it''s graded VS1, then it''s probably not a durability issue. That being said, I''d want to know how much of a margin there is between the feather and the edge. Can you ask the vendor?
Coati gives good advice. In an AGS or GIA VS1 I doubt it will be any sort of issue. Large/significant feathers can cause a diamond to drop to I1 clarity or lower if they threaten durability. Examination by a knowledgable expert can provide a definite answer.
The notion that a feather is a ticking time bomb sometimes goes around (possibly perpetuated by those trying to convert buyers to higher clarities
). Just remember that when the diamond was sawed, bruted and polished it underwent enormous pressure. Diamonds are subject to enough friction that they turn white-hot on the polishing wheel. Normal wear will not even come close to what they have already been through.
With that said, every diamond has natural cleavage planes. A knock the wrong way, especially at the girdle, can cause any diamond to chip or incur damage, whether there's a feather there or not. This is why having a good insurance policy is important for even the most flawless diamond.