Is the orientation of the thruster critical? I woul dlike to mount it with the cable position behind thruster instead of in front.
Hi @RobB, welcome to the forum 
The cable side of the thruster is its front, which has ~30% more thrust than in the opposite direction (as per the T200 technical details), because of how water flows around the shape.
Our BlueROV2 has the front two thrusters facing more backwards and the rear two thrusters facing more forwards, which gives an effect of roughly equivalent thrust both forwards and backwards, but turning while moving forwards is driven a bit extra from the rear (so the camera rotates without much panning), and vice-versa when moving backwards. Flipping all four thrusters would have similar performance, but the front-back bias when turning would be flipped (which is likely ok, but may have marginally less smooth video footage when turning while moving forwards).
If you’re using a different setup there will be different effects. As an example, if you only have two horizontal thrusters then flipping the orientation will change your performance from being better at going forwards to better at going backwards.