[plt-scheme] ffi vs. extension

I'm going to have a student work on integrating Berkley DB and, 
hopefully, DbXml into PLT Scheme next month.

When I updated the extension for GDBM a while back, I just followed the 
example and created an extension that's loaded using load-extension.

Lately, I've discovered FFI and was wondering about the pros and cons.

It seems that with FFI you can "require" the library instead of using 
load-extension.

Is each better suited for different purposes, or just two ways to do 
the same thing?

Which is easier to use?

Thanks.

--phil--