I agree with SpringHalo, these are just normal BL motors with sensors(hall sensors) so they can monitor and adjust the speed precise. this is common available in commercial BL servo motors.
I must also say that their build looks so terribly assembled, that i would never buy anything from a company that shows off so poorly made stuff. theyre probably very good at electronic engineering, but not at building systems. they probably spent several hundred hours on electronics and software, but not a dime on proper enclosure or pressure-sealing.
(i work with ROV parts, and subsea electronics/mechanics for oil/gas industry, so ive seen and built alot of electronic systems like this.)
the OpenROV looks 100times more professional than this in my opinion.