Since the Rebug team released the first 3.41 CFW in spring 2011, a few years have passed. Further releases followed from teams like Rogero, Habib, Ferrox, Evilnat and a few others.
Rebug no longer exists and only Evilnat has stayed on the ball to this day.
The CFW can be installed over any other CFW and is of course ideally suited to be installed after a Downgrade. The ability to go online with the CFW and play game backups from an external NTFS hard drive are certainly just a few notable advantages.
Here is a small excerpt from the features of CFW 4.90:An update from an older CFW version is usually unproblematic. Simply copy the CFW onto a FAT32 stick and install it via the XMB.
A newer version of the CFW has now been released. There is more information about it in this post.
If you are looking for a different firmware, regardless of whether it is original or custom, you'll of course also find it here.