The soul crystal ring can be energy-converted; even when energy-converted, it can still store items.
Its greatest benefit is that the Nascent Soul can carry it along, and it can even be stored inside the body.
It's not to say that a normal mustard seed ring cannot be carried by the Nascent Soul, but the Spiritual Objects that the Nascent Soul can carry are very limited and must be held in hand to be taken away.
The soul crystal ring can be energy-converted, allowing a large number of Spiritual Objects to be stored inside without occupying the hands of the Nascent Soul.
This advantage alone is enough to make the soul crystal ring the most desired treasure for Nascent Soul Cultivators, especially since during Nascent Soul Emergence, the Nascent Soul can mostly only carry its life-bound magical artifact.
With the soul crystal ring, other magical artifacts can be stored inside it, allowing the Nascent Soul to take them out whenever needed after leaving the physical body.
