Heyo, I've lived at Allen Court!
And yeah, the walls aren't that great for blocking sound. I'm a home student and I've found that there is still a fair amount of Home Students living in the halls.
And in Allen Court the flats have 6 rooms.
IMO, I think you hear more people applying to Ranmoor/Endecliffe since that's where the majority of Student Accommodation run by the uni is. However, there are a lot of independent companies around the area of Allen Court and St Vincents. Student Roost, Unite Students, IQ and a few smaller companies, if you're guaranteed to go to Sheffield it might be also worth to have a look at these options too