In order to make it easier for US customers to pick up a new Surface, Microsoft has introduced a new purchase scheme which offers them an interest free loan and an upgrade option after eighteen months.
The scheme, called Surface Plus, will be useful for consumers looking to pick up a Surface device who would have previously taken out a loan. They'll benefit from an interest saving. Customers who would have paid cash might also benefit, assuming the interest earned on their lump sum payment is more than the saving they could have negotiated on the Surface elsewhere.
The new device every eighteen months is more of a gimmick - especially as it values your device at just 25% of its initial purchase price. That's a pretty steep fall off for a machine which should easily run a four or five year usable life.
Still, if you just have to have the latest and greatest that Microsoft has to offer, this might just be the deal for you.
For everyone else, just stick with the interest free option and you can't go wrong.