If that is your only option (i.e. you didn't get IN anywhere yet), it is a great option.
I think last year's ACP went 10 for 12, with one person dropping and one person just doing poorly. If you get the class average (or even lower in some cases) you WILL get in. I've seen it happen to many of my classmates. I was a first year last year, and like I said, everyone who did the work got in.
It is most definately worth it.
Good luck, hope to see you there,