Please note that all seconds products have cosmetic flaws. In most cases, the flaw is really small and you can't find it unless you look really hard. Pieces which have more noticeable flaws will have higher discounts.
In all cases, there's no effect on performance.
Some product descriptions may have the reason for seconds mentioned, but this is not mandatory for all products.
P.S: No returns/refunds/exchanges/changes/cancellation of order possible on seconds items.