I've never bought a mystery bundle, probably because I'm still new enough to be filling out my fabric stash the normal way. I think maybe at some point in the future I'd be willing to buy mystery bundles but for a specific reason- I think we all tend to sort of have colors/patterns in fabrics we're drawn to and end up buying over and over. I think I'd use a mystery bundle hoping it would round out my stash with some colors or patterns of fabrics that I'd never think to buy for myself.