Tested Monster Channel version 1.1 build 91 on Ultra 4660 and didn't load after selecting Play. (Stuck on the loading bar).
On their website (landing page), implies "Coming Soon" to the various platforms including Roku so my guess is not fully operational yet or may be a defunct channel. The site implies you can contact them via facebook or email for updates. (select the appropriate icon, f or envelope). https://www.monsterchannel.tv/
The last update to their Youtube https://www.youtube.com/user/TheMonsterChannelTV/featured was about 9 yrs ago so difficult to say. Try contacting them from their site for a definitive answer.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941