my personal experience is in conjunction with a c4040.......
I have one of each. I prefer the manual controller for day time shots where wide angle compositions typically are more common to present themselves.
During night dives, when my personal style tends more to be for macro compositions, the ttl sensor is my choice. I found it to be reliable and consistent for that application where average reflectance and similar strobe to subject distances within the composition tend to appear throughout the scene.
Although the TTL sensor offers the user the option of both manual and TTL strobe operation on the same dive, if I had to choose only one, it would be the manual controller. The manual controller gives the user finer control, closer to the camera ( manual adjustments with TTL sensor occur at the strobe, situated at the end of what could be an extended strobe arm).