Yes my experience with the TC20E was limited to the "2" version not the "3". So not as relevant perhaps to todays environment.
Actually I am sharing a similar journey, as are many of us, in trying to optimize our shooting gear for wildlife, and with FX causing some disruption. It's important, as James mentions below to stay outside of wildlife's bubble or we won't get any shots. But with FX this can be a bit more of a challenge
I still plan on getting a mythical D400 and go shoot some unicorns with it