Everything on the supply side is unprotected. If one of the suplly wires shorts to the enclosure, GFCI will not protect you. If you incoming power cable gets exposed (or something cuts into it) your GFCI will not protect protect you.
A GFCI Breaker located as far up stream is the safest way to go. If its $60 ether way, go with the Spa GFCI. IMO