Erhardt & Nora's place is right at Greenmarket Square. This is about as central as you can get to the Cape Town City Centre. I always prefer a centrally-located place as it is easier to get to many activities and things. However, just note that in many central cities and urban areas, there are some trade-offs, such as some streets/areas can be sketchy when it gets dark.
Erhardt was a great host and always replied back to my questions quickly. His place has a great view of Greenmarket Square and I just happened to be there on a First Thursday, where the city hosts an arts/culture festival in the neighborhood with live bands at the square during the evening. I used the hop-on/hop-off bus, which was just a block away, so checking out the "Mother City" was very easy. The apartment was exactly as described and I would come here again.