What are advantages of 9mm FR Plug Wires

Every 10-20K depending on your application and how they look. The advantage of the FMS wires isn't something you will notice in the seat of your pants. Mainly, they are a better quality wire with thicker insulation on them that, when used in conjuction with other high performance ignition parts, should result in better mileage, throttle response, cleaner emmissions and better overall efficiency. The actual HP gain is debatable, and I wouldn't go running off to the dyno to see how I made out with a change of tuneup parts. It becomes more important the more modifications you have on your engine- on a stocker it's just a good idea to have them, you are less likely to have wires arking and stuff like that. If he's giving you a deal on them, put them on the shelf for later. You'll have to change them someday.