Shen Fei was disappointed in the Seraphim and Vegapunk because although the so-called Seraphim were powerful, their Devil Fruit abilities were not permanent. They used Green Blood as a consumable to gain Devil Fruit abilities, and once the Green Blood ran out, they would no longer possess those abilities.
With Vegapunk's intellect, he had still failed after all these years to develop a way for people to permanently possess Paramecia Devil Fruit abilities. Yet Mobius had, in such a short time, not only solved the problem of Paramecia Devil Fruits but also overcome the difficulty of granting someone a second Devil Fruit ability. The gap between the two was truly enormous.
As for why he was pleased, it was because Vegapunk's Green Blood was a good thing to him. So-called Green Blood was blood containing the lineage factors of Paramecia Devil Fruit users. It was this blood that gave the Seraphim their Paramecia Devil Fruit abilities.
In other words, by replacing the lineage factors carrying Paramecia Devil Fruit abilities within the Green Blood, one could replace a Seraphim's abilities. From that perspective, the value of Vegapunk's Green Blood invention was no less than an invention that allowed people to permanently possess Paramecia Devil Fruit abilities. It could let someone switch abilities according to the situation.
To Shen Fei, this was the real prize. As long as he obtained the technology for producing Green Blood, he could gain other Devil Fruit abilities without undergoing modifications. There might be other issues involved, such as compatibility with Green Blood or high production costs. Otherwise, this technology could have been widely adopted. But Shen Fei was confident he could solve those problems. With his current wealth and strength, there was no consumable he could not afford to use. He had already spent quite a