I did this too. If my experience of this was mimicked by the Time Capsule then the Airport + disk would be better.My first was an AirPort Extreme ca. 2007. I plugged an external USB drive that the unit shared over AFP and SMB. It could also share out a USB printer to the network at the same time with a USB hub strung onto its one USB port.
I still had the occasional Time Machine corruption issues back then and it was much quicker to attach the disk to Mac and fix (usually rm of the backup folder via Terminal) than any actions on the AFP mounted folder.