Best of Both: Quick-Release & Slow-Release Fertilizer
An electric composter's by-product is a quick-release version of a compost, which is naturally a slow-release form of fertilizer.
Synthetic fertilizers release nutrients very quickly, which, if applied improperly, can burn plant roots, or cause a "nutrient glut" which slows their ability to absorb other important nutrients.
Compost, on the other hand, releases nutrients slowly, over time.
Essentially, electric composter soil amendment releases nutrients quickly, in the form of its NPK rating, but will continue to break down over time, releasing other nutrients contained in the biomatter over a period of weeks as the bacteria in the soil decompose the organic matter.