I am seeing similar behavior on my Ultra 4660x with these three Screensavers. Each of them took me to the install screen (where an option to purchase for 2.99 was shown). It may be that these channels are free to watch/launch, but if you want the actual screensaver, you may have to pay 2.99. Not really sure though, because even when using "Preview Screensaver", it is reloading the purchase screen and not providing a Preview, so actually just may be having an issue currently. (One of them just showed me a blank image placeholder.)
These three are all created/developed by Nextin. Perhaps contact them at email@example.com and see if they can provide some info.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941