As far as I can tell, there's no difference in rewards between the two, it's just a tacit acknowledgement that you're up against opponents who'll probably know their stuff, or not
It's always nice to have options
Corners and edges are trickier but doable with the right training data
It can be played for only the cost of four ink via its Shift 4 keyword ability, and it also has the helpful Evasive keyword ability
The low mana cost of Shadowspear is what makes this card such a good answer: the equipment itself is just 1cmc and the ability -- which doesn't even need you to equip first to use -- is also 1 mana, making it super easy to tutor up and use it when combined with follow-up removal
One powerful idea is to combine Flash with Protean Hulk, where you Flash in Protean Hulk, let it die, search up Karmic Guide and Carrion Feeder, reanimate Protean Hulk with Karmic Guide, sacrifice it to Carrion Feeder for another trigger, fetch Kiki-Jiki, Mirror Breaker, use Kiki-Jiki, Mirror Breaker to copy Karmic Guide and sacrifice Kiki-Jiki to Carrion Feeder in response, which lets you reanimate with the Guide's ability