ScubaDadThree
Registered
Although trimix will give you less nitrogen, you introduce helium, which also needs to be accounted for in terms of decompression. I just ran two dive profiles through multi-deco using the Buhlmann ZHL-16-C algorithm, one using nitrox 25 and one using trimix 21/35. Since at the level of training required to do that dive agencies normally limit you to one deco gas, I used only oxygen for the plans. The two plans came out almost identical, with exactly the same run time.
For DCS planning, the primary safety factors are the deco profile and the gas (or gases) used for that purpose. It is more important than the gas you breathe during the bottom portion of the dive. Tech students often have a hard time understanding this.
The most important reason to use trimix on a 145 foot dive is to avoid narcosis. There are a few agencies that require trimix at that depth, and narcosis, not DCS, is the reason for it.
I had narcosis at 105 ft. in a Blue hole in Florida. That was why our Instructor took us there. So it would happen again on the Big O. Trimix would make the dive much more enjoyable.