I've got two machines, both Resmed BiLevel and had to decide between the S9 and the Aircurve VAuto. The bag was the deciding factor as I felt that the VAuto case was more funcitional, especially when I had to carry it. The carry strap can be put around the perimeter of the bag and can be tightened so that it fits almost like a glove. I used this to drape it over the handle of my wheelie suitcase and it fitted very well. This was essential as sometimes I had to walk a fair distance wheeling my suitcase with my backpack on my shoulders. The size of the VAuto compared with the S9 (with humidifier) was also an advantage but I rarely used the humidifier function so maybe I could have got away with the S9 stuffed into my backpack.
I had six separate flights and had to use the machine on the outward and inward legs of the Perth/Heathrow trip. For the other four flights, the machine was just extra luggage to be carried. I took it on board. Sleeping with a PAP machine on a plane is interesting as there isn't that much space to put it. I was in business class on the Qantas 787 Dreamliner and I had to place the machine very close to the aisle. The power plug in the lie flat seat didn't hold my Australian plug securely and it kept coming loose. I solved this by putting it into my UK adapter plug which, by design, holds in place very well.
Hose length can also be an issue and I wondered if a shorter hose would be a good idea. However, would this compromise set pressures?
After six nights in London I flew to Dublin and had ten nights in the republic. I'd hired a car so the issue of the extra bag to carry disappeared. When I flew back into the UK, I also had a car. For the majority of my journey I used Airbnb and power supply was not a problem. I did spend three nights on a canal boat and worried that they might not have the inverters and connectors to make my machine run properly off their batteries. My fears were groundless but if you do contemplate plugging in off grid it is worth checking out the power supply and connectors.
Overall, while I would have been happy to have one less thing to carry, it worked out well. This is now a fact of life and I should just get used to it.