As you likely know, with Amazon now owning MGM+ a direct add on subscription via Amazon works perfectly, which is how I roll over here. Been able to grab some great old movies in their catalog to replace my busted old DVD copies :)
I know you have no issues with Amazon, but I am not risking my account as I order too much stuff from Amazon.
Plus, I have access to MGM+ through my cable provider, so no chance I would pay Amazon a penny to get it from them, even if downloading were safe.
From the start of the Amazon module till just recently, with the notices and bans, it was no concern to download from Amazon.
Like I said, for some reason, MGM+ is not a module, yet HBO/MAX, Paramount+, and Starz are. But we do know that in the past, MGM+ worked using the DRM MPD downloader. So either a separate module to fix it, or hope for a fix in the DRM MPD downloader.