Exactly! The clauses are swapped around but the meaning stays the same: I saw an angel / of that / I'm sure = I saw an angel / I'm sure / of that.

"Of that I am sure" & I'm sure of that are the same. However your example sentence is different. The difference is "Of that I am sure" would come after a statement "I saw an angel, of that I'm sure". But "I'm sure that" will come at the start of a sentence as per your example "I'm sure that I saw an angel"