I've only ever seen KDM. Here are my impressions.
KDM is very thorough, intelligent, and though I've seen others call him 'cold' or 'disinterested', I
a) Didn't come there for sympathy
b) Found him easy to connect to. We laughed a few times over the course of the appointment.
KDM's general attitude is, "oh, yes, I've seen this a million times before, I understand it perfectly", and some people have a very emotional reaction to this. The idea that someone might actually know what they're talking about can be earth-shattering, especially for long-term patients. Some people get angry - how can you know, no one knows, how dare you claim you know?! - and others burst into tears. I gave him my Skeptical Eyebrow, but that's just because certainty isn't my particular emotional 'hot button': sympathy is. So we got along quite well.
The moment the appointment was over, I could see the more analytical part of his brain take over: it was like I had been filed away and therefore dismissed as a physical presence. Again, he was never rude to me, and I didn't take it at all personally!
KDM will test for everything, and I mean everything. He's very particular about his tests, where he gets them - has done a lot of personal research in terms of which labs get the same results consistently (I have heard from others that he has sent labs separate samples of the same patient's blood, just to determine whether or not the results are consistent.)
He is expensive, but only in comparison to your GP. For a specialist, his prices are very reasonable - but expect to pay a lot out-of-pocket for testing if your insurance refuses to contribute. Your testing will cost five or six times as much as the initial consult itself... or more. If you discuss finances with him, however, he is willing to adjust how much he tests for at once, or use another lab you have located if it is cheaper, or so I hear.
Once he has the data, he attacks whichever problem he sees as most severe. He uses whichever methods have good data: allopathic, alternative, it's clear he doesn't care so long as it works. You'll see cutting edge stuff you've never heard of along with a supplement you could obtain from iHerb, along with lifestyle recommendations like drinking a lot more water.
When you see him again, he'll reassess: you might start attacking the next problem down the line, or continue with the first one if he feels it hasn't yet resolved.
You have to take the good with the bad, though. His schedule means he's in and out of the States at seemingly random intervals, which has negative consequences for patients who try to see him in Reno and patients who try to see him in Brussels. His staff is scattered because they are overworked, and their response time is atrocious as a result - unless you say you have a health emergency, in which case (I have been told) they are very fast to get back to you.
Wait times for diagnosis were rough for me. I'm used to bloodwork coming back in a week, and genetics analysis taking a month to six weeks. My results from KDM came over three months after my appointment. As someone who has an illness that isn't well understood even by my family and friends, it was clear they kept thinking I'd been taken for a ride, or even that I was hiding my data because it showed nothing out of the ordinary - because no doctor here in the US ever takes that long to get back to you, no matter how busy they are.
Speaking of American things, some of KDM's recommendations are difficult to obtain in the US. With a little detective work you can figure out most of it, but I've just accepted at this point there are some things I won't get my hands on. For the rest, I would recommend searching here on PR before beating your head against a wall as I did; there are lots of recommendations for how to obtain unusual meds. In the end, the abx was easiest: I just found a reputable Canadian pharmacy and they shipped it to me.
Last but not least, KDM changes his protocol dramatically every few years. A lot of people could take exception to this. On the contrary, I think he's one of the few non-dogmatic therapists out there who is not so emotionally invested in his treatment plan being THE 'right one' that he refuses to change it. Instead, he shifts his protocol as new research comes in, and I feel that this is the mark of a good practitioner with an open mind.
In the end, would I recommend him? Yes, without reservation. He's a good guy, doing good work, at reasonable prices, and he really is quite brilliant. If you can deal with the long initial wait for info, and the headache of trying to locate what he recommends, and the headache of communicating with his overworked staff, then you're going to get an excellent practitioner and a sensible, workable treatment plan that has a decent chance of making you feel better. Though I've just started some of his protocols, I've heard from other, longer-term patients that they have experienced marked betterment of their condition through working with him. I know of one person who went from being bedbound to being back at college part-time, which is just incredible, though not typical.
I am sure that there are patients who have not improved by working with him. I hear them mentioned, but I seldom see them on here. There are also a few who consistently ask for 'proof' that his methods work. He publishes once in awhile, and he was part of the Canadian Consensus group. His published research plus patient testimony is the only 'proof' we have; and since no practitioner has 'the answer' in regards to ME, it's the best we're going to get. In the end, you have to make the leap to decide to see him or not, though to me, whether or not one ought to see an ME specialist of some stripe is a non-question. If it is at all within your means, you must do so. GPs have no earthly idea, nor do endos or neuros, despite this disease really being in their respective wheelhouses. Finding someone ME-literate to work with is essential to our well-being.
Hope some of this helps, and good luck,
J