Usage refreshes its recommendations on a daily basis. When your instance count increases, Usage buys RIs. When it decreases or changes, Usage sells RIs.

Our RIs are actually more flexible than SP. There is no commitment and if you want to change region or instance type, Usage will buy the old type and sell you the new type.

We chose RIs because AWS allows us to buy and sell RIs. There is no marketplace for SPs at the moment.