It's an alternative, but provides no new functionality. The truth is while owned by Meta, Mapillary has the best street imagery coverage of all three street view platforms. I provided millions of images for all platform so far, but here's some feedback.
If I had to rank them:

1. Mapillary integration with iD and JOSM and has the most configuration options and most active community. I dislike supporting any Meta platform, but for OSM's sake I think this platform works the best.
2. KartaView, which also has nice integration with iD and JOSM, but the community is smaller and the coverage is not as thorough.
3. Mapilio is the latest, but for now I don't see any new features and we are yet to see how this platform develops and how adoption works.

Fortunately all three platforms are integrated into iD, so editors have the option to use whatever works and has coverage for the area.

@unsaid0415 @mapilio

Mapilio: The map editor superhero. It helps users edit and enhance map data, and it's now teamed up with OpenStreetMap's iD Editor for seamless collaboration. Plus, it's powered by a UK-based nonprofit yet company.

Mapillary: A street-level imagery company owned by Meta (formerly Facebook). Different heroes, different backgrounds! 😉

I said something similar last time this was posted.

What didn't work well about Mapillary? Asking since I'm new to this.