It's a nice little bonus II gives you for depositing a good week with them-
If you give Interval International a good week they give you a bonus week. The bonus week is called an Accommodation Certificate. You can use this certificate to reserve villas of any size if they are available. One of the best use of bonus weeks is in the last 60 days of a timeshares use date. At that time, called Flexchange, you can use your AC for ANY week you can find. All the best weeks are there if they have availability. Otherwise you are often relegated to using your bonus week in shoulder and off seasons. Which works for us since we're retired.
They are good for a year, and I think they cost $399 for a two bdrm, but I am not sure of the exact pricing. I just pay whatever it is since it is way cheaper than a maintenance fee.