Instead of being half-demon, only 1/4 of your blood carries the power of the legendary dark knight like Nero.
While this might seem like a detriment rather than a benefit it is not, for human blood can nurture demonic power and make it grow. This has allowed Nero to match both Dante and Vergil despite being in his mid-20s while the sons of Spada were in their early 40s.
You start off weaker compared to Demon hybrids like Dante and Vergil but you grow in power much faster and you have greater potential.