Rinse the sago pearls under cold water to remove excess starch., In a medium pot, bring about 4 cups of water to a boil., Add the rinsed sago pearls to the boiling water, reduce heat to medium-low, and cook for 15-20 minutes, stirring occasionally until the pearls turn translucent., Drain the cooked sago pearls in a fine sieve and rinse with cold water to stop the cooking process. Set aside to cool., While the sago is cooking, wash, peel, and chop the ripe mangoes into chunks., In a blender, puree 1 cup of the chopped mangoes until smooth, adding a little water if needed., In a mixing bowl, combine the mango puree with coconut milk and sweetened condensed milk, mixing until well combined., Add the cooled sago pearls to the mango mixture and stir in a pinch of salt to enhance flavors., Taste the mixture and adjust sweetness by adding more condensed milk if desired., Scoop the Mango Sago into individual bowls or cups and top with additional mango cubes for garnish.