I think this way of looking at it is valid, although I don't personally like it very much because it generates a large amount of e-waste.
Regardless, using your model on this device: it costs $725, and if you buy now, won't ship until September. So if you assume 2 years from the device starting today, that's about $35/month.
Regardless, using your model on this device: it costs $725, and if you buy now, won't ship until September. So if you assume 2 years from the device starting today, that's about $35/month.