I agree with
@kensuf and the Fathom requirements to have AN/DP prior to going to CCR. I have no issue with all helium based courses being done on CCR, especially with cost and availability of helium where it is today. That said, Mod-1 is not the time to be learning bottle handling and gas-switching techniques and learning that you don't want to be in the water for more than an hour at any point in time. AN/DP is not cost prohibitive to do on open circuit since it is done without helium and I would strongly encourage anyone thinking about bypassing AN/DP on open circuit to re-evaluate.
Helitrox is a nothing course. There is no new information in terms of gas density, gas planning, decompression planning, or actual diving skills/techniques that you shouldn't already have from AN/DP *a third variable in gas calculations is not "new" in my opinion*, but you really shouldn't be learning all of that while you are trying to learn how to dive a rebreather. For those that already have AN/DP I have no objection to doing Mod-1 on Helitrox since it makes those 4-5ata dives much safer.