My Ecoboost F-150 (twin turbo 3.5 V6 for those that don't know) comes from the factory with a wideband O2 sensor behind each turbo. I use the Torque app on my Android phone and monitor A/F, boost levels, intake temp, etc all from my phone's screen mounted on the dash when I drive.
I have about 36k miles on it so far and am very active on various F-150 forums as well. I have seen many folks go over 100k miles on these trucks already and have yet to hear of anyone having an O2 sensor problem or issue. They are mounted maybe 18" behind each turbo so they may or may not be in the most ideal location, but they seem to work pretty well and have good longevity thus far.
Just my thoughts.