Can someone explain the difference between the two? I bought the Promise but now am wondering if I need the time machine. My work requires me to hold a lot of photos but I need to easily access those photos as well. Any advice?
The Apple Time Capsule hardware device is primarily designed as a backup target for OS X Time Machine backups. It can somewhat function as a NAS storage device like the Apollo Promise, but it is very slow and nowhere near as full featured for file sharing as a NAS like the Apollo. The Time Capsule is an Apple Supported device for Time Machine Backups, and good for that purpose, but it a lousy NAS device IMO.
If your main usage is for file/photo sharing/access, the NAS is a far better solution.
@lularoekatiewillis The Time Capsule is going to be limited to 30-35 MB/s of throughput to its hard drive, which pales in comparison to any good NAS. It does a great job at what it does, but if big files are going to be stored then looking at a NAS like the Apollo or a Synology is a better choice.