Boxfish 360 is a professional 360 camera rig designed for underwater use.
I’m not sure but I think 2520 is the vertical resolution, so the resolution in equirectangular format would be 5040 x 2520, which is higher than 4k.
Here is a sample video:
The video quality looks impressive, although hopefully the stitching could be improved.
For purchase inquiries, please contact Boxfish Research directly. Here is the official website. Thank you very much to Jim Jensen (the very knowledgeable moderator for the Photo Sphere Community on Google) for bringing this to my attention!