I would say the best is gonna be DIY, either for root tabs or column dosing (it doesn't need to be EI)
For premade/commercial I would use other Thrive or Tropica
For cheap root tabs I would really use osmocote if none of the above 3 work for you... Is far better than Seachem or API
But I haven't used every option that is out there and would use an aquasoil instead of root tabs.