PRO subscription: Nag screen with upgrade prompt is not a good idea
I think that it is not a good idea to implement a feature like "Lock block" and offer it to PRO subscribers in the context menu, and then when the user wants to use it, have a popup with an upgrade button appear, stating that this feature is only available for Business users.
I mean, it doesn't make sense to get a PRO subscription user to sign up for a Business subscription just because they want to use a generally useful feature, while they may not need all the Business functionality (user management, etc.) at all.
I don't think this is a good strategy to sell users the more expensive business subscriptions.
Business features should also be such, that is, they should perform business-specific functions. A feature as basic as block locking is not, and should therefore be available to PRO users as well.