I am a second year (going into 3rd year) and was a paramedic for 13 years before that. I worked the last 6 years of that time as a critical care flight paramedic. I often think about doing what you are talking about once I am out and done with residency. I maintain my paramedic and my FP-C still for just that reason.
I do some CE education and may have the opportunity to work limbo (PRN, maybe once a month) for a flight service here in town.
Honestly, it is a mixed bag. I will say that even flight services now seem to be getting more and more patients who likely did not need aeromedical transport. My opinion (for what it's worth) is that this stems from the saturation of and aggressive push from air medical providers encouraging EMS agencies to contact them - which leads to more patients being flown as a "precaution" due to mechanism. This is also happening at hospitals too. Air medical agencies and their parent hospitals are catching on to the fact that transporting sick and injured patients and drawing them into the system can pay (in some cases, in others it is a losing proposition). So hospitals are becoming aggressive with interfacility transfers...whether it be from one of their outlying facilities that flies under the same flag, or from another regional hospital that they have marketed to with the line, "we have a helicopter, if you ever need to transfer a patient, we can get there fast...".
Anyway, I digress a little bit, but the point I am trying to make is that in some shifts, there may be 2 out of 3 flights where you just shake your head, and at the end of the mission, realize the advanced level of care you COULD provide really made no difference for that patient, as they did not need it. You became an expensive taxi. So I just wanted to give some perspective. This varies by region and flight service, so making sure you target services with good safety cultures, good mission profiles, and progressive management is important.
Now with all of that, I will say this, even with all of the flights where I may not have felt like my services were needed, I was always happy that I was there in case I was needed, so please don't mistake my little rant as a criticism of the patients, the ground providers, the hospitals, or the work. It was really just a fact of life.
I said earlier 2 of 3 flights may be just an expensive taxi ride, but sometimes on that third flight you and your partner get to really pull a rabbit out of your hat and, as my old medical director used to say, "save the lives that nobody else can save." I am not so bold as to think that I am the only person in the world who has the skills or abilities necessary to do the work that I have done, but I will say that there have been more than a few calls where my partner and I looked at each other afterwards and knew that we got a chance to save a life that day...I am sure you know this already, but nothing really replaces that feeling. You probably get that feeling in the ER, but when it is just you, your partner, and the pilot with that patient, and you're managing 3 pressors, titrating sedation, adjusting vent settings and coming in for final at the hospital with the patient (relatively) stable and in 10 times better shape than when you picked them up...it is just a really satisfying feeling. That's about the best way I can describe it.
I can't help you directly with the question you asked regarding the logistics of getting on with a flight service as an MD or challenging the paramedic course, but feel free to PM me if you want to know any more about the nature of the work, or what to look for in a potential service to work for. There are services out there that I would work for in the drop of a hat, and there are services that I would turn and run as fast as I could. It can be difficult to tell the difference when you are looking to get your first flight gig.