Sorry I come to this a little late in the thread-been on a train.
As somebody who is actively teaching triox courses via IANTD's Advanced recreational course, I am seeing many more divers become interested in having some helium in the mix to reduce levels of narcosis.
Triox is hyperoxic trimix- i.e the o2 percentage is higher than 21%. For IANTD triox then mixtures must contain at least 24% 02 and can range from 32/15 for 30m dives to 25/30 for 45m dives and should have an EAD of no greather than 24m. For a 45m dive then 25/30 would give you an EAD of 21m and a quite acceptable P02 of 1.34 for your target operating depth. For contigencies the mix is acceptable down to 48m - 23m ead and 1.41.
The triox course is designed around divers making the transition from recreational sport diving to taking their first steps on the technical ladder. Limitations for the course are a maximum depth of 48m and a maximum mandatory decompression stop obligation of 15 minutes. Decompression gases maybe upto 100% 02 but personally I would consider 50% to be a more appropriate gas for 40m dives as it provides many more options than trying to use 100% and you can get on it at 21m if required.
From a diver prespective if they were considering doing Advanced Nitrox then I would seriously look at Triox as a viable alternative for diving in the 30-45m zone. The course structure is identical and covers the same skills- kit configuration, propulsion methods, shutdowns, oog, dsmb use, use of a stage and stage handling, deco procedures, emergency procedures etc.
Divers who qualify with Triox have the advantage that they can choose to use either Triox or a weak nitrox mix for their diving. Some divers might reflect that 15minutes of deco is a disadvantage against unlimited deco- bear in mind that the course is aimed at developing the diver and that you need to walk before you can run
I think that the majority of divers would agree that in this range Triox has many advantages of nitrox mixes in terms of levels of narcosis. Whilst Triox does require students to be able to control ascent rates and carry out decompression stops then this is no more onerous that carrying out similar stops on Nitrox.
As intermediate training prior to moving onto trimix then I would recommend the course as the core skills required give an excellent foundation for more advanced training. The course also encourages the divers to think as a team and look at team solutions to problems that might occur underwater- as Brian says there are a number of different options open to you
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Andy - if you want to see how the course works them pm me- always got a need for good safety divers --though you would need a trimix or triox cert
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HTH
Ian