Giving a Control user the ability to black out a users screen is extremely dangerous, and will lead to abuse of your free trials.
Please see this video for reference: https://www.youtube.com/watch?v=_drmu_2Ump4
A very common scam lately is obviously done by giving a malicous user access to your PC remotely. With the ability to blank out the screen, the malicious user is able to login to your bank account, etc through your browser without you realizing it.
Then, if you have two factor, they claim they will send you a code (since they are "your bank"), and the end user typically will GIVE them the two factor code, and allow them to login to their bank.
This is extremely dangerous, and should not be allowed - especially in a free trial version of the product.
Customer support service by UserEcho