Hello Mike,
thank you for your interests. Here is a summary of the pros and cons of both implementations.
Because the mcproxy is written in c++, it needs more main memory and so it is less suitable then the igmpproxy for low power embedded system.
There are no known bug in both implementation, but igmpproxy is much older and because of that the more used implementation. It is probably more bugfree than mcproxy.
Mcproxy supports the group management protocols IGMPv2 and MLDv1, this mean it handles IPv4 and IPv6 multicast, while igmpproxy handles only IPv4 multicast. In the near future the mcproxy will be updated to support IGMPv3 and MLDv2.
The mcproxy supports multiple multicast routing tables, this mean you can run more than one multicast proxies on the same machine. Igmpproxy doesn't support this feature.
Igmpproxy and mcproxy are only management software for the multicast routing tables of the Linux kernel, the throughput depends only on the Linux kernel and the machine itself.
If you have further comments or question don't hesitate to connect me.
Best regards,
Sebastian