I am testing my Twog with an airspeed indicator consisting of two MS5611 pressure sensors. Results are promising, but sometimes I don't get data from one or both of the MS5611s after power cycling the system. A repeated power cycle normally cures this. When both barometers get running, they run consistently.
The Sparkfun SEN-10121 IMU seems to work fine every time, and I have no problems with Auto2 flight.
I use <subsystem name="imu" type="ppzuav"/> in my airframe file.
I am on Paparazzi version 5.4 and use my own DIY twin-barometer module.
I looked at the I2C bus with my logic analyzer, and it seemed the protocol was almost filled with data, leaving almost no idle time at all. Excluding the barometers module showed that the IMU packs the I2C protocol with data. The SEN-10121 has ITG3200 gyro and ADXL345 accelerometer.