No downside for Apple users. There’s some downside to Apple because it reduces lock in.

In a q and a a reporter even asked Apple a question about this directly

But the person who asked the question, Vox Media’s LiQuan Hunt, came back with a valid complaint, saying that his mother can’t see the videos he sends her. It all comes down to a lack of interoperability between iMessage and RCS, both messaging systems that could allow higher-quality images and videos — if they worked together. If you’ve tried to send a video from Android to iOS (or vice versa) using your regular text messaging app, then you know that your videos come out completely fuzzy on the other end. Cook’s suggestion to fix this annoying issue? “Buy your mom an iPhone.”