First, the location is superb. The flat is a very short walk to Marylebone Station (Bakerloo Line) and a moderate walk to Edgware Road Station (Circle and Hammersmith + City Line), which gets you quickly to all the museums and London landmarks. There's also a Tesco (grocery store) right around the corner. We also discovered our absolutely favorite place for breakfast within 10 minutes, the Marylebone Cafe. Oh yes, Regent's Park was a healthy, but close walk as well.
Second, Helen was extremely kind and quickly responded to a problem we were having with the shower. No points were deducted for it, though, because we could still shower with the secondary, handheld head while the issue was resolved.
We did deduct a few stars for issues we felt would have made our week-long stay more pleasurable like a way of addressing the dampness and a house (flat) book explaining how to get the most of our time in the property. We're confident Helen will consider them.
In summary, this is a great location for getting around the city and with a few adjustments, it will also be a great place to feel comformtably at home.