If you stick to non-consumable items then the plugin can handle it. You only need to think about databases if you plan to use consumable items and care about multiple device usage as you would be using local storage where only one device knows about it.
If you install the app on 2 different devices you would see the following : local data such as scores and progress lost on the second device, because it's stored locally (and the user would expect this anyway), but due to IAP plugin and account use they would see that they have bought the unlock store content on both devices.