There are big differences.
- CLEPs don't have as much prestige as APs, and most top colleges don't accept CLEPs. CB says 2900 colleges accept CLEPs but they are lower-tier colleges
- CLEPs are taken through a computer, scored automatically. I'm not sure when you can take them but you can certainly take them more often than AP
- There are many tests for the CLEP, I think there are 34 tests
- CLEPs are much easier than APs and only MC, few might have essays