Not needed on most Macs (non Retina)
I didn't get this through software update for my late 2011 MBP. Downloaded and installed it, but 1/2 way through installation, I thought "I have a built in 1GB ethernet port, so why am I installing this?" I can't imagine wanting to use 2 ethernet lines at the same time.
Thunderbolt to Esata would be great, but I don't want to pay the current $200 to $300. I bought an Esata drive from Other World Computing with an Esata adapter also from them to use with a 2008 MBP. About a year later they report that this adapter doesn't work with MBPs in the 15" range (couldn't figure out why my date kept corrupting)
Now I have a 3 TB drive that I can't hook up without spending 200 to 300.
Hopefully these will come down in price.