If the Berserk is anything like the Nomad Dagger, it will be an outstanding choice for your son. Since he already has a VG and polished Mutant Cell, the Beserk would be a few boards less overall than the Mutant while still being a few boards more than the Misfit.
Now, I haven't thrown the Beserk but the Nomad Dagger gave me a very clean look up front with a predictable arc motion that was hard to beat. It also made it very easy to tell if I needed to throw something stronger, weaker, or stay with the Dagger.
From what I understand, the hybrid cover on the Beserk is similar to the Dagger. Plus, the Camber Core builds off the Rotary Core by offering better energy retention while still offering great hitting power. Also, the Beserk is just cover and core- no filler material. Overall, it could be a great ball to fill in the gap for your son.