Heh
the diamond give timer isn't coded in sorucepawn, its somewhere in the war3dll extension
it should be 1 diamond per minute(from the top of my head)

Edit: recheck diamond give interval

C++ extensions have more power and can handle real objects
sourcepawn plugins can be easily+fastly developed while being aware of Memory leaks/crashes(if Not doing something terrible wrong)
sourcemod extensions are basicly used to extend the functionality of sourcemod itself
I personally prefer extensions for big projects than using plugins, because doing stuff with Objects is far more powerfull and "cleaner" (imagine a OO war3source)

Probably intresting for you: http://forums.alliedmods.net/showthread.php?t=143279