Today's ad has 12 yds of 60" wide 'Roc-Lon" muslin (the bolt) for $24.99. Both bleached and unbleached. It sounds like it would be good for some backings, and also for making practice sandwiches. (I'm determined to improve my freemotion quilting!) Is this a good buy, and if so, would you suggest the bleached or unbleached? Thanks!