I'm not familiar with the 4 degree ignition advancer mod, what's the gain with this one?
Engines are generally tuned to run off the crappiest petrol available, so they retard the spark to give the best chance of a good ignition.
As we have reasonably good quality petrol in the UK, this is unnecessary and advancing the spark allows more complete combustion of the fuel/ air mixture.
Basically it gives better running and improved throttle response.
The most important thing when fitting it is to ensure that you DO NOT let the timing rotor turn anti-clockwise when you're undoing the rotor bolt, otherwise it will throw the timing off and (at worst) could result in catastrophic engine damage.
There's various suggestions online, putting it in first gear, holding the brake down, using a screwdriver (or custom tool), but, personally, I used an 8mm spanner wedged between one of the timing rotor teeth and the bottom left of the rotor housing to stop it turning anti-clockwise as I unscrewed the bolt.
Note that the bolt may well be threadlocked on, so I had to use a breaker bar to get enough leverage.
Also use a Sharpie to put a couple of lines on the timing chain and the inside of the casing to ensure that it stays in the right place.
This is the one I bought:
https://www.ebay.co.uk/itm/163936332980You will also need a new gasket, this is the best priced one I could find:
https://www.ebay.co.uk/itm/Yamaha-FZ6-N-FZ6-NAHG-YZF-R6-2003-2009-Oil-Pump-Cover-Gasket-5SL-15456-00-5/153893393187