The pros of installing a fmf head pipe are a little more top end hp for the powerbomb and little more lowend tq for the megabomb, both make the bike a touch quieter too.
The cons are they're not a good bang for your buck, they cost a lot and only add a little power at the very top or very bottom where you don't spend much time while riding.
IMO its best to do a pipe, programmer, air box mod and AIS delete at the same time, you get the most hp and best rideability this way.
I simply unhooked the exup cables from the servo motor instead of spending money on a servo delete.
If you don't get rid of the AIS you will get back firing when you let off the gas, it doenst hurt anything if you can stand the racket.