Considering the vast number of Mac hardware, monitors, graphic cards and macOS versions, it’s impossible to guarantee that your specific issue on your hardware will be solved with SwitchResX.
SwitchResX is distributed with a free 10 days trial, exactly because of this. During these 10 days, you can try the program and you have access to the support to help you in your trials.
You are not required to register SwitchResX until you have tested the needed functionalities and get it working on your own hardware.
In this case you will get a lifetime license, which will never expire, and will be valid for all future SwitchResX 4.x versions. This is not a subscription, and you are not required to register again for future 4.x upgrades.
However, once registered, there's no refund granted, because this lifetime license cannot be revoked.