The owner was responsive and the description of the apartment is basically accurate. There are issues which keep me from recommending it to others, though. You can judge whether or not they're important for your situation.
The location is indeed close to Euston Station - perhaps a five minute walk. This means that while in the unit you can hear (and feel) every single train going through that station. The apartment is located on a street which is busier than one would expect and quite near a major road. You can easily hear many trucks going by throughout the night. Finally, on most nights of our 6-day stay a large group of people gathered on the street in front of the building and held parties well into the night (at least through 0300). If you care to join in then that could be great. If you'd like to sleep, it's less good.
The flat itself is as advertised. Having four bedrooms is very nice. Each room is small and some have no wardrobes so you live directly out of your luggage. The common area is one room (as shown in a picture) with a small couch and a folding table in the kitchen with folding metal chairs. There's not sufficient room for non-folding chairs. Guest parties of more than four people shouldn't expect to comfortably spend time together in this area. The benefit of the unit are the bedrooms (assuming you don't the noise sources discussed above). If you plan to be out of the apartment most of your non-sleeping time, the common room is less important.
The positive side of this location is easy access to many Underground lines through the three different stations that are within a 5-minute walk. That makes getting almost anywhere in London easy. Regent Park is a 10-minute walk and that's a beautiful place.