Ok, I agree with all points except one, I don't see how Terrarium does anything to security on an Android device.
And then, Terrarium is definitely a really bad application. It is definitely not legitimate, which is why it's not on the Play Store. Besides, there are loads of ads that pop up out of nowhere.
If you still want any other such app, I would suggest you to look at Stremio. It's basically like Kodi, but I like it better because of it's intuitive UI. It's available on the Play Store, and I'm sure it's legal because it is using a loophole.
Stremio was originally made to curate content together from a person's Netflix, Prime Video, Hulu, HBO, iTunes and Play Store collections so that you could watch stuff anywhere and on any device. But you would still have to actually sign in to your accounts, and pay.
Here's the catch: Stremio allowed people to create Community Developed Add-ons: which are disabled by default in the app. And BINGO! You have add ons for everything from RARBG to PirateBay. All you have to do is: go to Settings of the app, and enable Community Add-ons.
Kodi is pretty similar, and definitely more popular, but I feel it doesn't have a good UI, at least on Android.
Tom, I'm absolutely shocked by your post here. I've always considered you hip and knowledgeable; but as the old saying goes, the world will never know your ignorance until you open your month. In your research of this topic, did you or your expert discuss the specifics of copyright laws specific to streaming vs downloading digital content directly to a personal electronic device? Based off of your responses here, I would have to say no. Before we had fast internet speeds, downloading movies, music and other digital content was the most popular form of sharing digital content. It was also highly illegal as copyright laws in most countries made it illegal to possess copyright digital content on a person device that was not purchased or obtained legally. As internet speeds increased, sharing digital content via streaming became an overnight wonder, and also a loophole to copyright laws, as streamers don't possess the digital content on their personal devices; but simply view it remotely. Terrarium Developers have no legal liability as they have only developed an app that "scrapes" the internet to requested content. The developers don't possess this digital content themselves. I agree that the possessors of illegal digital content have a legal liability for storing such materials on their personal devices, but this would not be an issue of the developers, nor the viewing streamers. Copyright laws are specific to possession, and if you disagree, then your concern is with the structure of the law, not the developers.