After more than five years and almost 20K hours on the blower, it was time to look for a replacement for my old Resmed S9 Autoset. I tried both the newer Resmed S10 Autoset and the Philips Respironics Dreamstation. Both are very nice machines, but I found both of them lacking vis-a-vis my old S9, so I chose another S9 Autoset, which CPAP.com fortunately still carried in stock. Main reason being that I for my physiology can get my AHI down to a .3-2.0 range with the S9 (especially compared to my 3.9-5+ AHI on the Dreamstation). The S9 also can better serve as both a main and travel CPAP (i.e. two CPAPs for the price of one) and - after you get familiar with its buttons and dials - is easier to operate and fine tune than both the two newer machines. It also does not have that recurring nuisance airplane prompts of the S10. Why Resmed's engineers had to "reinvent the wheel" with the S10 instead of building upon the S9 escapes me beyond them having an incentive to sell us both a main and a travel CPAP. My main issue with the S9 is that its algorithm can be a bit aggressive (as is the S10), occasionally doing some pulsating huffing and puffing, which is probably good during A/Hs and might be the reason I can get such low AHI. But it is a bit bothersome when it doesn't realize I'm awake.

This review is intended for people who've never used an Auto CPAP machine and are considering buying one.
I had previously been using an old ResMed machine since 2008 when I was first diagnosed. It was a real workhorse even after all those hours but it was time to replace it.
My only regret here is that after "testing" the Auto feature, I found that it wasn't comfortable. The AutoSet only provides air flow when inhaling, not when exhaling. It's a natural breathing feeling but I guess after all these years, I had become used to sleeping with the constant air flow.
As a natural "mouth breather" before using a CPAP machine, I found that the only way the Nasal Masks felt comfortable is with the constant pressure. Without that, I feel the need to "gasp" through my mouth.
In the end, I changed the setting in the machine to regular CPAP. Which is OK and wouldn't knock the machine on stars for that since I knew what I was getting and I figured that a machine with both options would provide some choice.
No, the machine loses a star because I'm disappointed in how little data is provided through the on-screen display. I would have expected more info here and even in the clinician mode, there isn't much info. I guess you need the software and a card reader to get anything more useful.

I am coming from a basic CPAP only machine (REMstar Pro M Series) provided by my insurance over 5 years ago. I was sleeping fine with my old machine, but wanted two have a second one for travel/backup. Before purchasing the S9 Auto I did a lot of research and decided to try upgrading to an APAP. The S9 Auto can be set to run in CPAP only mode so if I did have issue with the APAP setting and it cost very little extra than the CPAP only model.
Because this is just my second unit I can only compare it to my older system.
The S9 has updated looks, controls, and screen but roughly the same bulk (less depth, more width, similar height). Even the power supply is a similar two cord with mid brick.
When I used it for the first time I noticed how much quieter it was. My old machine made so much noise I could not really listen to anything at bedtime without making it too loud for nighttime use. With the S9 I could still hear the news even though the volume was low. Now the noisiest part is my mask exhaust.
My previous unit had auto start/stop but I had an issue with the auto stop shutting down the airflow during sleep. With the S9 the auto start and stop work correctly in identifying when I am wearing my mask.
The slimline hose that comes with this unit works as well as any hoses I have had in the past. It connects easily to the S9 and to my regular mask.
I have only been using the S9 for about 10 days and have not noticed any major changes (good or bad) from using and Auto vs a regular CPAP in my sleeping. This unit does track actual data as apposed to my old unit which basically just tracked usage. So the color display and the info it provides is good.
With the help from sleep boards I was able to gain more knowledge about my S9 Auto and the data collected. That data has allowed me to learn a lot more about my actual sleep habits and take my overall satisfaction in getting this unit from good to great.
My only slight issue is that the plug that goes into the back of the unit only can only be inserted in one orientation with the cord facing downward. I liked in my older unit that the cord could be turned slightly so that the was not aimed straight at the nightstand.
The travel bag that comes with this unit is of good quality. It is made to carry both the base unit and the humidifier attachment. Since I do not use nor have the humidifier the bag is a little bigger than I would prefer, but there is plenty of space even if you do have it.
I now have two machines I am comfortable in using. It is too early to notice any sleep benefits nor comment on the longevity. The improved display, quieter sound and overall looks are nice upgrades. But the information about my sleep may prove to be the most beneficial.

I purchased two S9s. One is used solely for travel and replaced the Zzz-Pap CPAP which worked very well for around 5 years of extensive travel use. The Zzz-Pap is no longer available and my unit was becoming intermittently nonoperational due to the known Err 2. I found the Zzz-Pap easier to travel with because of its smaller size and integrated power supply.
The S9 is a superior machine in terms of quietness, features (auto, exhale relief), and a non-medical device look/feel. I find breathing more natural and not a continuous rush of air. It has lots of other features, optional integrated humidifier, data reporting and accessories, which I don’t use. It also makes a decent travel machine and comes with a laptop-style carrying case to store the machine, humidifier, hose and external power supply.
I don’t check-in luggage and don’t want to carry a third bag, even though CPAP machines are allowed above and beyond the carry-on allowance for a bag and personal item. The S9 standard external power supply is the size of a brick and not conducive to my travel. The S9 itself is very lightweight (1.8 lbs) but the standard power supply weight/size defeats this benefit. Resmed has a significantly smaller 30-watt external power supply which I use with my travel machine. The S9 is not as compact as the Zzz-Pap and the protruding push dial seems fragile and awkward when packing it in my carryon. I wrap the S9 in a T-shirt, and use an Eagle Creek Pack It Half Cube to store/pack the 30-watt power supply, slim line tube, extension cord, and Resmed Swift LT Nasal Pillow mask.
This makes a very lightweight and physically compact travel system which I have used in Europe, US/Canada, and Asia. Although it is not as compact as the Zzz-Pap and requires carrying an external power supply, the S9 provides me with better therapy and sleep.