My wife has a set of Tek 3, I dive it when I take my Zeagles for service. They are great regs and very good breathers. I only took them down to 100ft and even having them adjusted almost to the hardest setting - 1/4s off the - setting and having venturi on - I have no issues with how they breath. Some people say they are more expensive than the original DS4/XTX 50 but at the place we were getting them at it was the same price.
I do like how they route on doubles, the hoses are not bent as much as on my zeagles.
The coldest I ever had them was only 36F and they perfomed flawlessly, you might get a bit colder in the ocean over the winter ?
Overall we are very happy with them.
You might also want to consider DST with the 5th port + XTX 50 , they would route like MK25s. Or if you dive warmer than 40F you can also consider Mk25/G250V