The protection of the spell not being countered when mana from Cavern of Souls is used is a major plus
A planeswalker will make you consider how much potential damage you can hit it for
With those reprints come new tools, synergies, and, of course, exciting new Commanders to build around
When looking at this, you want to evaluate if you would want a card in your deck that draws you 3 cards and discards one, and if you want a 5 mana flier that bounces stuff
If there is a set of Secret Rares in the set with a huge number, putting them in the Reverse Holo slot makes packs dynamic and keeps them rare without making them unobtainable as a complete set
Thats because many rare (or higher) cards can hold significant value, and may even rise in value as the years pass