I've a Elite Drivo already from a last year and all this time without exception - when connecting with Zwift on Mac OS X computer via Bluetooth Smart and doing freeride (or race, groupride etc.) I have very low resistance - especially on a 0% grade. Because of that I will spin out even at 50-11 gear and basically can't achieve much more than little over 400 W, maybe little bit more on climbs. So sprinting in races is basically impossible. Curiously, this problem with Zwift Bluetooth connection doesn't show up in Zwift workout ERG mode. I can do workout intervals at high power in ERG mode just fine using Bluetooth connection.
At the same time my Drivo works perfectly fine in Zwift via ANT+FE-C in both simulation and ERG mode. Also my Drivo works perfectly fine in the Elite app via Bluetooth Smart slope and ERG modes. And my Drivo works perfectly fine in Trainerroad via Bluetooth Smart.
Hopefully Zwift finally fixes this old and extremely annoying bug as the Bluetooth connection is definitely preferable indoors over Ant+FE-C. With Bluetooth the connection with computer is much more reliable (and works with iPad, iPhone) and trainer reacts to changing gradients much better than with Ant+FE-C. This is probably due to Bluetooth better error correction algorithms and much higher refresh rates than Ant+FE-C 1Hz signal.
For now one has to resort to Ant+FE-C for races and sprint training and Bluetooth for ERG workouts.