xfps will not be as precise as using key/mouse on a pc game. it will feel sluggish compared to pc, but it still should be very usable. especially when you set the look sensitivity in game to max. kinda like the smartjoy frag on xbox1.
for the longest time i would only play racing games on the xbox1(same thing on 360 now) cuz i couldn't get used to the controller with fps games....too many years of pc gaming i guess. when smartjoy frag came out, i got it right away. i loved that thing cuz i could finally play so many games i missed out on. i feel the same way with the xfps.
thing is, i don't like to lose or get my ass kicked every time i play any game. without a key/mouse, i could fumble around for awhile with a controller but i would always get owned and give up in frustration. i need a key/mouse for 360 fps's. without that, i just wouldn't play them.
it's not a fair argument to say a key/mouse compared to a controller on a 360 would be just as much of a advantage as using a key/mouse compared to a controller on a pc game. a controller on a pc fps game would be no competition(no matter how "used to it" sombody is). but a console is so different. when i used a key/mouse on xbox1, i really don't think i had an advantage over others. i never dominated, i just competed and had fun. i wouldn't quit cuz i was frustrated. i know there are people that will dominate with a key/mouse on 360, but there will be more people that dominate with a controller. so many people are already so comfortable using a controller. on a console, i think a key/mouse is a great thing cuz it will bring so many more people to the games. it will raise the competition level.
i can't wait for the xfps to be released. 1st thing i'm gonna do is buy gears of war, call of duty 3, and rainbow six:vegas. then i can finally start my love affair all over again with my 360.