Sales on Happiest Baby app

We were lucky enough to buy a secondhand snoo from a couple that never used it. They actually never even registered it so I was able to register it in my name. (I believe they had paired to it via the app though so I was surprised to see that it wasn’t registered. How is this possible?).

I am due at the end of March. I was just looking online and saw that the app is currently running a promo for $9.99 for up to a year. Do I need to jump on this and just eat the cost of two extra months or does this promo happen regularly and I should wait and see if it runs again before my due date.