As far as I know Spool makes kits only for old 81mm OEM and N1 pumps, while Supertec does for all pumps, except maybe HKS and Reimax. Also Supertec makes a high flow N1 splined kit with wider back plate, so pump flows 6 liters per minute more.
Black painted kits are Spool, genuine metal finish for Supertec. So Tomei, Jun/Nitto/Greddy pumps owners have only a Supertec option.