I have an ethernet adapter and a thunderbolt -> DVI adapter.
They both work.
As far as the ethernet adapter goes, it does the job, it just works. The CPU usage it isn't great and it chews a fair bit of power when on battery but i haven't compared to any other gigabit NIC.
I'm not unhappy with either.
I'll use the ethernet adapter if at my desk and want more reliable speed. It's definitely faster for time machine, even against 802.11AC.