If this were 4-6 weeks ago I’d seriously consider opting for the refund and scouting around further than Lenova. The processor on that system is impressive for the price. But I’m not sure I’d opt for Dell these days. I’ve had- or been responsible for-- several Dell systems from Win 3.1 to XP. After Win 95 my experience of support and call-out engineers was not particularly happy. That said, I paid more for my Dell Win 95 desktop than for most systems available today so I suppose we’re getting what we pay for. Think I'm going to go for the C560.
FAQ number 3 here shows the difference between the Mainstream and Extended support models. For the most part it makes no difference to consumers whatsoever as the things lost are primarily for businesses.