In general, if an app isn't available in the "Streaming Store", there's a reason. A quick search turns up some red flags about the legitimacy of this "service". You can't add Android apps (APKs) to a Roku device (if that's what you're asking). What you do with a Chromcast or Fire TV device connected to a Roku TV is independent of the Roku TV.
I can add that Roku doesn't support the Chromecast protocol. They do support other casting protocols. Some Android phones (Google Pixel, many no-name basic brands that use basic Android) will not see a Roku as a castable device.
Can also add that a Google search had a story that they were raided by Argentine police and shut down about a month ago. Sounds like they were an illegal IPTV service, and there are major crackdowns worldwide against them. Operators have been convicted and jailed and fined millions of dollars. Some areas are now going after the users, too.
https://www.reddit.com/r/FireStickHacks/comments/1g074wu/magis_tv_is_down_raided_by_police/
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