I started the Jack Talty course a year ago when I got my first concertina. As a total beginner who hadn't played music since I was a teenager, it was really excellent. Jack has a very methodical approach to teaching, and it has given me a solid foundation. I flew through the beginner course, learning quickly. I'm most of the way through the Intermediate course now, and it's been great too, but a steeper learning curve, so I've gone through it much more slowly. I also branched out quite a bit after getting a foundation in the beginner's course, so I haven't been as devoted to the lessons as I was early on--but that's a good thing, because he gave me the foundation to be able to branch out and learn music on my own! I think it's been a good value for the amount of material there, but I will probably cancel fairly soon, as I'm no longer using the course as much. Hopefully I can figure out how to cancel!
I've done Caitlin's sample video lessons and enjoyed them. but Jack's approach is a better fit for me. I also did some lessons through OAIM, mainly because I forgot to cancel after the free trial ended. Learned some good tunes there, but the instruction isn't nearly as thorough as Jack or Caitlin's course.
I live in a tiny remote community in Alaska, so in-person tutoring isn't possible, and I've been really impressed with how much I learned from Jack's course.