m-of-n is cool but is it useful to many people? Is it substantially more useful than chargebacks? It isn't for me.

Hmmm...I must be missing something. It is, at least, as useful as chargebacks, because a chargeback is a subset of m-of-n. I suspect companies will spring up to provide the service (and probably instant payments and other stuff) for cheaper than credit card companies currently charge, and with less intrusive credit history checks and such.

You can do chargebacks much later and for a far greater range of reasons than you can practically do with m-of-n transactions.