The short version
Royal City is a self contained high rise complex on Nguyen Trai. It is attractive to residents who want managed access, shops and leisure in one address. It is less suitable for anyone seeking ordinary Hanoi outside the lobby, because the complex can make the surrounding city feel distant even while sitting on a major corridor.
The convenience is genuine inside the development. The compromise is scale, traffic and dependence on lifts, garages and internal routes. Look at the exact tower, the journey to the street and the cost of services beyond rent. A glossy shared facility does not tell you how the flat itself will age.
I would choose Royal City for a defined managed lifestyle, especially during a first year in Hanoi. I would not choose it while pretending it is a typical local neighbourhood.