It depends on which shaders you are trying to import. Many shaders on shader toy will not simply convert into ISF shaders. You’ll have to do a bit of coding to update them. Additionally, adding variables, sliders, buttons, toggles, inputs, etc, is a manual process which the ISF Editor import feature cannot do.
It’s going to be more work than plug-in play FX. And you also have to take into account, that the people who uploaded their shaders to shadertoy or sandbox may have spent hours, days, or even weeks in writing those shaders. Make sure to keep and check their credits written in the top of their code and abide by their terms, as well as, give credit where credit is due.