We enjoyed staying with Simon and Charlotte so much that we booked a second visit before we even left!
Simon was traveling during our visit, so we unfortunately didn't get to meet him. Charlotte, though, was a terrific host – incredibly friendly, accommodating, and helpful (both providing restaurant recommendations and reviewing British vocabulary).
Their flat is very nice, and in the middle of a great neighborhood. The flat is only a couple of blocks from the Overground, and within an easy walk of two different Underground lines. We mostly got around by walking or taking the bus, though, which we found very easy.
We can't recommend staying with Simon and Charlotte enough.