yeah, having advancements would make it unfair for the other players.

I finally grabbed my copy of ODST today and got Reach installed.
I was in RAGE before since my original copy of ODST I bought (second-hand) was scratched to bits and my 360 couldn't read the disc, but I kept it since I could use the Multiplayer disc to play online with friends.

Will try out Reach a bit later, hope it's good.