Drobo + Time Capsule

Question

I have a Time Capsule that I use for Time Machine, and am thinking about getting a regular entry level 4 slot Drobo to hang off its USB port as shared, non-Time Machine disk space. The Drobo appeals to me because I can expand it as my needs grow, and because it has RAID-type functionality built in. I figured that I could also unhook it from the Time Capsule and attach it to an individual machine should the need arise.

Have you tried this before? How has it worked out for you?

Edit: Just to clarify, I was not looking to use it for Time Machine data. The Time Capsule itself has plenty of disk space for my Time Machine backups. I'm looking to add network based storage for general use (archiving videos, rarely used disc images, etc.) I don't really need the performance of a Drobo FS, so I was looking to see if I could save some money with a regular Drobo.