Hi, I posted earlier this week about regs I ended up buying two used Poseidon Odins second stage one for me and the other for the wife as they were reasonably priced I took them to my local dive shop to have them serviced and put on my first stages which one is a Tusa and the other is an Oceanic, the lady told me that I could only use them with Poseidon 1st stages as they run on higher pressure, Is she correct as it seemed she was only interested in selling me a whole Poseidon set up which is more than I can presently afford, I even asked If I could buy a 1st stage and she said no only the whole set up, I know if I search I can probably find a used 1st stage, but before I do I would like to know as I thought I could add them to any 1st stage, Thanks for any and all advice.