I have used many of these as well. My experience is that in US and Canada they post as either cash or some other credit to the folio, and you get full Marriott points and night credit.
In Europe they reduced my room rate by the Bonus Bucks amount. In Huntingdon England and Hamburg Germany. And they used a lousy exchange rate. Since they reduced the room rate, I did not get full pints for the stay but OK maybe it is fair that way, after all I got a discounted rate.
In Tokyo they posted as a credit AND they used an exchange rate favorable to me - a $50 cert credited at 6000 Yen or 120 to the dollar. The going rate was only about 108.