It's absolutely perfect for what I want. I've got three 3Tb and two 2Tb drives connected to give me a total available space of just under 9Tb and I'm using less than 3.5Tb so plenty of space.
I have my entire iTunes library on there and I'm also using it as a repository for my downloads folder. I rarely delete anything I download so I've got installation files for pretty much anything I've installed on my Mac over the years.
My iTunes library is streamed out to a couple of Apple TVs around the house. Both can be playing at the same time without any problems or speed issues whatsoever.
One thing I have done is to replace the feet on the Drobo with
these as I was getting some vibration through onto the desk which I didn't like. I didn't expect them to make any difference but they really have, it's practically silent now. All I hear is the actual disks chattering away when it's busy. There obviously is a fan running but it's so quiet, I don't notice it above the ambient sound in here.
For backups, I use Backblaze. I was able to transfer the licence state from the old iMac so it didn't have to copy everything up to the cloud again.
I also have a 3Tb Time Capsule which I'm backing up just the SSD to (this is also used for my MB, my lad's MBP and the "family" 27" iMac we have). In addition to that, I have another external 2Tb USB-2 enclosure which I've partitioned into two x 1Tb volumes. SuperDuper! clones my SSD onto one of the partitions every night and I've told Time Machine to use the other partition as well as the Time Capsule. Time Machine is quite good like that, you can give it multiple volumes and it alternates between them.