I think they're fun, and a very reasonable way to acquire a collection of coordinating fabrics. There's no law that says you have to use all the pieces from a jelly roll or charm pack all together in one project. You can mix and match with other things from your stash, supplement with solids, mix it up with prints from a different collection.
There's nothing inherently less traditional about quilting with pre-cuts. They lend themselves very well to a great many traditional designs and techniques.
Not everyone has a lot of time available to enjoy their hobbie. IF using precuts gets someone through the stage in the process that is a sticking point for them enjoying and completing a quilt, then it's a good innovation for them.
As far as cost, that issue has been hashed out at length in earlier threads here, but when it comes right down to it, if you want small quantities of all the fabrics in a line, you will be hard pressed to purchase them as separate cuts for an equal price, once you factor in the losses you take from crooked cuts.
RST