As someone who enjoys learning about different faiths, I think I might have gotten the wrong Quran translation

Assalamu alaikum, everyone. Hope you're all doing well. So, I'm really interested in theology and I like to study various religions, even though I'm personally an Orthodox Christian. I ran into a bit of a snag though, which seems common when trying to find authentic holy books from different faiths. I bought what looked like a really nice Quran from a bookstore. When I read it, I noticed it had some extra notes and paraphrasing under the main text. I looked into the translator, Maulana Muhammad Ali, and found out he was part of the Ahmadiyya movement. From what I could find, it seems many Muslims don't consider them to be within mainstream Islam because they believe in a prophet after Prophet Muhammad (peace be upon him), who is believed by Muslims to be the final messenger. Should I look for a different, more widely accepted translation of the Quran for my studies? (I'll probably keep this one too, just for reference on their specific views). I've had this happen before with other religious texts too. Also, just out of curiosity, could someone explain what the Ahmadiyya movement is about? Is it seen as a separate branch or something else within the Muslim community? I don't mean to disrespect anyone's beliefs, but I usually try to avoid books from groups that are considered outside the mainstream, since they sometimes present their interpretations as the standard for the whole religion. Jazakum Allahu khayran for any insights.