I have installed a rate gyro board (Adafruit L3GD20) on my ROV control board to attempt to circumvent the severe EMI problem from the thrusters I experience when using a compass board for heading hold. Bench testing (see picture) has proven the gyro to be totally free of EMI interference, even when I hold a thruster right next to it. Yeah!!!
I realize I will experience drift with just a gyro, but that may still work for my purposes.
With a lot of bottom time hours now, I have learned that some form of good heading hold is mandatory, especially when there is current. The current drag on the tether is large and is always trying to turn the ROV (seems always in the direction you don’t want it to go).