Hi Charlie, welcome to FISD.
Both helmets are ok for basic approval and with minor adjustment in the Anovos one.
For levels 2 (EIB) and 3 (Centurion) The crl states specifically for the Vocoder:
The vocoder must be integrated into the helmet, and not a separate piece
As I know, the Shepperton Battle Spec has the vocoder as a separate piece. (Can you confirm this with the vendor?)
The Anovos Helmet will need a few adjustments for L2 and L3 too but they're easy fixes like change ear screws , modify the hovi tips mesh and some paint details.
In my personal opinion, the Anovos one is easier to upgrade for high levels.
Cheers.