I have an Atmos Pro, which I have had for a couple of years now. It's a very good computer. Most of my Dive Buddies have them too. They are made by Pelagic, and are very similar if not identical to some computers sold by other companies like Genesis and Oceanic, if I remember right.
It's not like a Suunto, which are made by someone else. Suuntos are much more "conservative" than the Aeris computers. In the great lakes last summer, my buddy's Suunto was going nuts because the dives were deeper and longer than it liked. My Atmos Pro was very calm, and I had no trouble with it at all. I'm not that aggressive, and in my opinion the Suuntos are much too conservative. Suuntos are very popular, quality instruments, but to me, this is a major disadvantage, not something trivial.
There are two things you need to be aware of. One is batteries. When they go, they go. You turn your computer on, it gives you a low battery warning, and then goes off, all in about 2 seconds. The upside of this is that they are quite easy to replace and you do NOT lose your data, like if you lose batteries in the middle of a trip. Get some extra batteries at Walmart or Radio Shack, and always, always, take them with you on the boat. You also need a quarter to remove the batteries and some silicon grease to lube the oring. I don't replace the oring every time. The little kits from the dive shop have the oring and two batteries, but are expensive. Plan on replacing batteries after about 50 dives. (Milage may vary).
The second thing only applies if you are diving Nitrox. After a nitrox dive, you have to confirm the nitrox % between dives, or it reverts to 50%. This, too, is very easy to fix if you remember it. It's just sort of a nusance.
You should be happy with the Atmos Pro. If your mate is getting a computer too, you should get another Aeris, not the Suunto. You'll be too imcompatible in the conservatism department.
