I think the biggest strength of an interview training course (non specific to medicine prep) is that it will give you confidence to approach the interview. If you go over some easy ways to work in your strengths or you get used to talking about the challenges in rural healthcare, it invests your interview performance with a natural confidence that is lacking otherwise. Of course, you don't need to attend a course to help with that, they just make it easier.
If you're looking to get some building blocks to practice and to familiarize yourself with the process, then they're pretty good. But most interview questions are repeated year to year, so you generally won't be asked anything surprising or outlandish. Get some general practice in and you won't need to prepare responses specific to questions XYZ
As for MedEntry, they're just a bunch of <edit, mouth soap etc.>. Coming from someone who believes in a laissez-faire free market, that should tell you something.