Its the same principle as a sand filter, that is used on most pools and large ponds now days. Although dont see them in salt tanks very often, but more and more, very large tanks, like 1000g+, are using them.
Freshwater sand filters have metal parts and use silica sand, which would cause a variety of issues in a salt tank. Salt sand filter can be very expensive but they are very effective from what I have seen. The cost versus the benefit just makes these unfeasible for small tanks sadly, but k1 is the solution to that.
These arent detritus filter though, they do one thing really and thats to increase your nitrogen cycle capability. By being self cleaning, they maintain maximum surface area for the bacteria to colonize. Its the same premise as putting tons of live rock in the tank, but generally more efficient.
Detritus needs to be cleaned out via other methods though, or it could clog up the system and cause parts of the bed to slow or stop moving. The whole bed of media needs to stay in motion continuously, which can be one of the primary challenges of these kinds of filter.