Interesting - I hadn't seen libpnet before. I was recently working on an experiemental project doing deep packet inspection in Rust using libpcap, which doesn't have very mature Rust bindings yet - the basics work, but it's a bit rough around the edges. libpnet looks like it has a much nicer Rust interface, and does some more things for you as compared to libpcap, which gives and takes &[u8]s and nothing else.

However, libpnet doesn't have two very useful things, as far as I can see: Reading/writing packet capture files, and the ability to use BPF filters. The first in this case might be useful mainly for testing, but the latter seems like it might simplify a fair amount of their code.