I was in Brussels for a couple of days so I thought an apart hotel would be a good idea and it was.
The First Euroflat is located next to Schuman, at the heart of the European Quarter where the EU buildings are located.
To move around: Schuman station, 100-200 meters from the hotel door, has trains (including international trains to Luxembourg) and metro lines that go directly to the center in 4 stops. You could also work to the center in ~20-30 minutes if you wished. I would say that's a very convenient location.
To hang around: there is a very large park that is lovely when the weather is nice in Brussels. There are some small supermarkets including one carrefour that has extended hours and opens on sundays. And when it comes to nightlife the Stevin street and adjacent streets have one of the best offers of pubs and restaurants of Brussels, so again a very convenient location.
The hotel staff was correct, with fast check in and out but I did manage so avoid some big crowds that were dropped and pick up by group busses at the door. Had I done my check in or out at the same time than one of these groups and I would have probably had to wait much longer.
The room is very big, with a small kitchen, a separate table with chairs (2) for eating, and a lot of storage space. There was nothing in the kitchen but you could request it to be stocked if you want to cook. The room was not as clear as in other places, showing its age (carpets, quilt, furniture in general).
I did miss electricity sockets to charge my two phones and laptop sat night. there is only one accessible from the bed (for the phone that I use as alarm clock) so I needed to charge the other phone in the bathroom and the laptop in the kitchen.
I was also there during very hot days (exceptional in Brussels) and there was no a/c in the room so they provided a fan and the room remain very hot. I know Brussels so i won't complain about hot days.
Very good value and the good location and space make it very convenient so I would return.