You would need to purchase subscription only if you are planning to install Notezilla on Windows PCs and wish to sync all your Windows sticky notes with your phone. (Automatically syncs notes every minute)
If you just plan to use the Android app on your phone and do not intend to sync with PC then you don't have to purchase the subscription.
Let me explain you the 2 models of Notezilla so that based on it you can take your decision regarding the purchase.
We have 2 different pricing model, Notezilla (Cloud) and Notezilla (Non-Cloud). The non-cloud version is one time payment. So you don't have to pay again every year for the same version Notezilla 8.0. You can use it for ever. The Non-Cloud version will not allow you to sync between PCs and also sync between phones/tablets.
However, if you are planning to sync between your PCs and devices, then the pricing is subscription basis. This allows you to install Notezilla on any number of Windows computers as long as they are all synced with the same sync account.
With the optional cloud synchronization feature, you can automatically sync sticky notes between computers every minute, access them from any smartphone (iPhone, Android, Windows Phone, iPad etc) or send sticky notes to any contact across the globe.