Marie,This instructor is NAUI, not TDI.
I know some old timers who do large single tank and deco bottle for deco dives around 130-140ft. You think no redundancy is a good idea for 180ft?
To me, the kit issues become a bigger thing with this deep of a dive.
As you are taking AN/DP (and Heliox?), do a gas calculation for an 185’ dive for 13 minutes.....include Calcs for lost Deco and buddy gas....... see if a single 80 and a 40 are within standards.......