Don't know if these are any good, to any of you. I picked up a set today and they work good. Designed for motorcycle use, so not waterproof. Not a problem, to put inside a waterproof box.
They have an extra jack socket and cable, so that you can have another input at the same time as the intercom function, ie, VHF radio etc. Voice sounds over other input.
Tech details available, if wanted.