They both offer solid stats while being somewhat vulnerable to removal, which makes one or both welcome additions to many Cubes
If you're wanting to build a token deck, a Warrior kindred deck, or even just something that goes smashy-smash, mobilize cards are a great way to make it go that little bit quicker
Something to be clear about with the Fan Content Policy is that it is meant to enable people who are creating something
It cant trade your opponents commanders around the battlefield, but it can swipe a creature the turn after you cast it
Having access to this with cards like Sythis, Harvests Hand in the command zone means you cast an enchantment, draw a card, the enchantment enters, and you can play a land from your hand