Compared to most other sets that were used in TOS, the ruined outpost of Cestus Three had an impressive look to it. To my eyes, it didn't look cheap (relatively speaking). It didn't look like the standard studio backlot set.
I would have to say that the production people did a good job. Because, with the craters and ruined appearance, it was visually believable that a battle took place there. And what added to the luster of the set was that it was actually outdoors.
Yes. I always liked the episodes where the filming was done on location. If the production crew would have had to film Arena’s outdoor scenes inside a soundstage it would have greatly diminished my appreciation of this episode, in the same manner of Squire of Gothos, et.al.