I spent couple years shooting with 5dmk2 without any TTL because the old Mathias TTL converter that I had working with my 5d didn't work with 5dmk2. I really missed that feature for few months, mainly for fish behavior, but I we are capable to adapt and change our mind to shoot without that making the adjustments manually.
Since Feb this year I upgraded to 5dmk3 on Aquatica housing and started to use the YS TTL Converter/C with couple YS120. I am really glad to have it back. It is very reliable.
The only cons I have about that TTL converter is related with appertures over f/22 where we need to increase the light compensation using the dial in the converter, but it doesn't vary, I just got in mind the compensation for f/22, f/25 and f/32 and it became automatically for me.