The short version
Hoang Mai is a large south eastern district where older settlements, apartment projects, lakes and industrial land share a wide catchment. It is a local housing market rather than a single expat neighbourhood. Choose the pocket that fits your daily route, because the district name says little about the street outside the building.
The newer towers can offer space and services, while older lanes provide cheaper, more immediate local life. The trade is road dependence and uneven public space. Check drainage, school traffic and the route to work after dark. Hoang Mai makes sense for a south side routine, not for someone who wants to stroll into the historic centre every evening.
I would consider it for value and space, but only after visiting the exact lane.