Along with being smaller in general, the MARKs were designed based on feedback that once worn out, the Peltor ARC adapters had a habit of popping out at inopportune times.

Personally, I ditched helmet-mounted comms long ago, as have many professional end-users. Most guys prefer to take their helmets off whenever they get a chance--helmet mounted comms means that if you still need comms, you either need to keep your helmet on, have a spare headset, or remove your comms from your helmet, effectively negating the point of having there in the first place.

Part of the reason the new Ops-Core AMP is coming out is based on user-feedback from the RAC requesting a stand-alone capable version, and the AMPs are now modular so you can attach them and detach them depending on your use.

~Augee