I am not aware of a 50 Amp, 240 volt GFCI Plug - The spa should be protected by a circuit breaker - also, having a GFCI breaker feed a GFCI receptacle will not cause tripping of either device. Only ground currents will trip them.
I perfer the spa disco. 50 or 60 amp models mostly. 240 volt. self contained 3R enclosure. comes with a dead front GFI which is attached to the coil of a contactor. Feed it from a regular circuit breaker.
Re: Spa - GFI#86513 11/08/0302:48 AM11/08/0302:48 AM