I have watched Dave Donnelly via his French Light Dressage FB page and the Classical Dressage page which he moderates (and he does a good job of that).
He is in Landrum, SC and I’m a couple of hours away in Aiken, SC. I have a couple of light breed horses, so I went up to watch him ride for a day. I liked what I saw. The way his WS, above, described him seems right to me as of 2020.
You have to want and understand how the French think about making up a dressage horse. If you are an educated horseman who can also “take what you like and leave the rest,” I think he’d be a good guy to work with. On a personal level, he seems like a nice guy and easy to get with. Seeing him ride three, of varying degrees of training and strength, I can assure you that he is not hard on the horses. Watching lots of video as well, I think he likes to let them be expressive and his horses don’t go with a lot of tension in them. I think that’s a sign of horses who have been brought along with some care and skill so that they are challenged, but don’t feel like work is a grind; they feel seen and heard.
In short, I’d definitely take some lessons from him on a horse he had made up. I might do that on a horse of mine, but only after I personally went and watched him ride a few. Then again, that is what I do for any pro. If you don’t like or understand what you see, no need to go further with him.
PM me if you want and I’ll answer questions. Not sure I want to get into the DQ Mosh Pit here.