Yeah I am doing it right now and I can tell you that you most certainly get more than adequate training in all 3. There is substantial overlap in the 3 fields and my cohort and I are among some of the strongest residents in our institution. The same can be said at the other programs as well. The schedule is tough early on but like most other programs it gets easier as you become more senior. Anyone that completes this training can get it done from outpatient management to a cardiogenic shock patient in extremis in the Cardiac ICU when its done.
At the risk of speaking for a very diverse group: The end goal for a lot of us is to find a career as Emergency Physicians and Intensivists though I have seen many other things. I have seen primarily ED docs with significant critical care research going on. I have seen one doing EM, MICU and running an aeromedical EMS service. I have seen ICU primarily with per diem EM shifts. Lots of options.
The Internal Medicine training provides additional breadth as well as extensive exposure to the chronic conditions that are frequently managed in the ICU. This allows for anticipation of the clinical course on the floor and in the outpatient setting which can help guide management as we "captain the ship through the storm" in the ICU to quote JDH or send someone out of the ED with the hope they eventually follow-up. Six years for all of the options that the 3 certifications provides is not bad at all. The biggest sacrifice is the financial hit and continuing to be a trainee for an extended period of time.
