I think if you want to cut a 24" strip you want the very big one which they have at Joann's - 23"x20" wide so you can whoosh right up those 2 1/2" strips. I have one and I love it.
http://www.joann.com/search?q=June%20Tailor%20shape-cut
$83 bucks and I gotta say if you car cutting strips it beats moving the ruler and trying not to wiggle the fabric at every whoosh!