Normal βpaintβ orientated products will work ok on GRP, usually. They generally just need a bit more work.
GRP specific cut and polishing products differ by the amount of cut, the GRP cutting compounds especially are usually more aggressive, than the paint equivalent. But also, once you start moving on to coatings, GRP specific ones, (especially, marine, which many are) will have more UV protection than normal automotive for paint and may have a few more marine specific qualities for sea/sea life exposure.
When it comes to work horse cutting products, 3M have some very good compounds, GRP specific. (Farucla G10 is still very popular, too, for initial use after wet and drying, or harsh cutting, there are better these days, though, such as the much newer 3M product)
With any of these in GRP, it can be done by hand, but for cutting especially doing the whole car, either a DA or a rotary pays dividends.