there are more that a modded barrel and mag to the first strike. the bolt is modded, and the barrel is changed too.
the 'scope' is just a red/green dot that offers no magnification. I replaced mine with flip-up grenade sights. helps calculate drop for those FS rounds (plus looks awesome). You also might consider a multi-level crossbow sight.
the above pros/cons are fairly valid. However the marker doesnt NEED performance upgrades. It's not for people who like to lay down a hail of paint. I go out with 1 hopper of paint, and 1 130rd pod, and this lasts me 1-3 games. I only have 1 FS mag, and slap that in for those 'special' moments. (GET OFF MY HILLS)
sadly, mine isn't totally unique at the field. My friend and my wife each have a t9, and a t8. thats how much we love them.
Oh, and get a x7 g-36 sightrail for yours. the 'scope riser' that comes with t9's is a heavy worthless piece. Only lifts the scope 1 inch, and to use any optics, you need it 2-3 up.