I have a buddy that is wanting to sell me a slightly used (only 3-4 times) scubapro s600 regulator. He is asking for $400 for the setup... I have been diving with an Apeks ATX 50 and I was just wondering what the comparison of the two is? I've looked at several postings & have read good things about both. I am working with students quite a bit, but I also like diving for myself. I am looking for something that will be good for both situations. Anyone have any suggestions? Also, would this be a good deal?