A lace piece hairline is an illusion... but it's a good one.

Real hair growing out of skin does look different (you can actually see the hair coming right out of the skin), but most people have no clue and no one looks at you with that level of detail anyway. You also don't have to expose the whole hairline.

If you do things right and maintain the piece, you don't really need to worry about anyone detecting it by sight.