Their CSA system worked a little differently. Rather than a set "box" or a weekly share, prepaid subscriptions entitled customers to discounts that could be applied to the purchase of any kind or amount of produce at the farm stand or market. It was convenient, because you could choose just what you wanted at a given time, rather than on the farm's schedule. But, at least initially, it seemed less economical than a more traditional CSA, where you pay in advance for your full share and then figure out what to do with it. There's likely to be less waste and less 'produce panic' with the Siena model, however.
I happily signed up again for this year. For quality, variety, friendliness, and sheer beauty, I highly recommend Siena Farms.