There are many benefits to this approach and it is likely worthwhile.

Another downside is that you have a long cycle when it comes to assessing your churn. Yes, you'll see customers effectively churn by stop using your product, but when your customers are monthly, they are de facto making a purchasing decision every month. If they are annual, you aren't getting that re-purchase decision until the 12th month, when they have much more information about your service than pre-sale.