Marcia,
T23 outlined some conceptual facts about combo Inflater/Alternate second stage (octopus) units. I happen to agree that those units regardless of manufacturer or models represent trade-off. I won't say they are unsafe but safe use does require some level of training and buddy briefing. One inescapable fact is that they are not the mainstream configuration and the alternate second is the one piece of gear that involves interaction with your dive buddy almost always in a stressed situation.
Here is an old post of mine where I take my shot at the topic.
There are design differences in how the Atomic regulators are designed that let them promote a 2 year interval. Regulator service is driven by 2 big factors. One is seat impressions. The valve that controls air delivery in your second stage includes a soft seat and a some whats sharp orifice that seals against the seat. It's much like putting your palm over your mouth. The adjustment of this valve is very subtle and will make the difference between a regulator that breathes nice or one that free flows or breathes like a rock. As most regulators sit idle the orifice is seating into the seat and this delicate adjustment deteriorates as the seat develops an impression. The atomic folks went on their own to do some innovative stuff and created a regulator that does not leave the 2 parts in contact. That is the big swing point on the interval.
The catch is that they have no control over the second service driver, contamination. One bad dunking, one mis handled dust cap, a wet valve or contaminated tank can get stuff like salt water into a regulator and start corrosion and deterioration. Eventually parts are damaged and/or performance falls apart. The 1 year interval is also largely a hedge against corrosion. And there's not a lot Atomic can do to mitigate this except for some premium materials that are of dubious value in this case.
Other than that modern seals, correctly installed will serve well for any reasonable service interval. O-rings don't fall apart in a year.
Parts warranties are nice but there is no free lunch. You can still count on paying about $20- $25 per stage to perform the work. When I was shopping I looked at SP. A local dealer told be to expect $25. per stage and maybe another $20 for parts they change that are not in the free kit. In any case free parts do not equate to free service. A service kit may retail for a wide range of prices from about $7.00 to I'm not sure how much, but a lot more. For some users of some regulators at some point skipping the warranty and going on their own nickel makes sense. For the average new diver running with the manufacturers warranty program and having things checked if there are any concerns or suspected contamination is the way to stay safe.
In terms of regulator performance there are always some differences. In many cases they overlap within the range of the finesse of the set-up technician. As a new diver any of the top shelf brands will serve you well. Almost any diver will be perfectly fine with almost any regulator that is set-up right, it's hard to find junk. When you do side by tests you will no doubt sense differences and they may differ in totally different ways such as one reacting quicker wile another delivers with less effort. They are probably all fine and the big thing is that after a tank or two you will have bonded with it and it will feel natural to you. Going with as much regulator as you can afford in a brand you can get serviced locally is a sound way to go.
Pete
