"slightly accurate" is the correct description, though -- dead reckoning on a cell-phone-class IMU accumulates drift too quickly to keep objects anchored in space for more than seconds at a time. You need something (visual odometry, SLAM) that provides long-term stability, even if it has short-term noise or poor availability, to fuse in.

When this topic comes up, I'm always happy to share this incredible lecture from many many years ago about sensor fusion and dead reckoning and how you _cannot_ integrate acceleration twice:

https://www.youtube.com/watch?v=C7JQ7Rpwn2k&t=1401s (the whole video is incredible, but this timestamp is the magical bit)