The box from home depot has everything the Spa depot box does. It handles up to 60 amp, it is weather tight, and it has an extra spot for another breaker for power or lights. It has the GFCI breaker, and all grounding bars installed.
Since it is being installed outdoors away from the house, having an interference-shielded breaker is an un-needed feature. Both boxes have knock out panels/holes.
The spa depot box is very over priced. I have 2 people on my block with the home depot box and it works perfect right out of the box.