I bought my first pair of Air 1's in 1991 when Scubapro was selling out their stock at 1/2 price. I got the pair for the price of one D300. My wife and I moved our 109 and 108 to octopus use and have used the Air 1's ever since. They are extremely easy breathers.
They do breathe heavy and damp when fully inverted, but we don't do that often. I also had one instance of having a ripping side current cause damp breaths because the diaphragm serves as the exhaust valve and it is exposed from the side by the huge exhaust ports. I have never had an uncontrolled free flow nor failure of any kind.
My sons got certified at 10 and 12 and I bought used Air 1's for them. They have used them regularly for 8 years. The Air 1's breathe so easy that they would forget to change them from pre-dive to dive position when they first started diving. To them, the Air 1's pre-dive position breathed as well as the rental regulators they used in their dive classes.
I also have 3 D300's, a D350, and an early D400. Every one of the Air 1's breathe easier than the D-series regulators, not by a lot, but noticeably. All the D-series regulators breathe about the same. The Air 1's and the D-series use the same rebuild kits, so there is no difference in serviceability.
The only regulator I've used that breathes better is the Scubapro Pilot. I have several of them in good working order. In my opinion, they are incomparable, but I freely admit I haven't had occasion to use much except Scubapro for the last thirty five years or so. The Pilot is obviously not an option for almost anyone because they are nearly unobtainable and nearly impossible to service unless you do it yourself.
I purchase Air 1's when I see a particularly nice one or get good deals. I have a number of them now, certainly enough to last the rest of my life. You should get yours serviced and use it. It's as close to the Pilot as you are ever likely to get. You will love it.
