We recently stayed for 3 nights at the 550 Flinders St.Adina & found the staff very friendly.
We had a one bedroom apartment & found it clean & roomy enough for us.
The balcony was great as we could open the doors. Only negative, & it could be quite a biggie for some was the very noisy air conditioning on top of the next door building. Not very noticeable in the day but very noticeable at night. For that reason only I guess we'd hesitate to stay there again.
Pool was quite tired and not very deep (1mtr) but gym was excellent. Very handy to the train station & bus depot and the trams are just across the road.