I think it depends a lot on what you want to get out of it.
Mauro is well-versed bonsai artist. Well known of course for his work on pines, but he is really good with all types of conifers. I am not sure about his broadleaf work.
Assume he might assist you, but you will do the brunt of the work. Decide whether you want styling, refinement, deadwood etcetc input from him.
If I were to have a workshop with him I would look at trees I do not know how to elevate, where I am unhappy with certain design aspects. Ideally I would bring a tree left alone for the last growing seasons so there is lots of healthy & material to work with. I know enough about styling to know what to prune and what not, so I might actually do a light cleanup of the the tree and I would uncover the nebari. This way it is easier for him to quickly assess the tree.
The challenge is with wiring. I never wire out my trees before a workshop, and will do it during the workshop, as I find I still can use advice on my wiring, which is best gotten during the process (For me). I know some will go to such a workshop bringing 4 trees, once for every morning and afternoon. All wired out. Get the tree discussed, work on it and afterwards get the artist to help you fine-tune the layout. Ask the workshop organizer what the setup will be. If there is only space for 1 tree to be discussed, this would not make sense.
The place where I do most of my workshops has this as a setup for a self-work workshop, with numbers normally 10-15 persons present:
(the day might start with a demonstartion or lecture byu the artist on their expertise). The the artist will go through the room and discuss the trees on the tables one by one with the owner. The first trees are discussed in most detail, and the generic information is then slowly reduced as he moved from tree to tree. Then everyone starts working on their trees, and the artist will walk around, spending 5-10 minutes on average with everybody. This means you will get his time once every 2 hours (!). I normally have multiple trees, and I make sure that when the artist comes around to me, I have another tree ready to be discussed, so I get 2 for one. I get a quick assessment of the work done so far, and I get a review of other material which I might work on later.
Take time off tedious work on your tree to follow the artist around. Look at the material other people bring. Make mental sketches and development choices on those trees and then listen in on the advice of the artist. Compare that with your mental notes. Which things are different from your ideas? ASK why choices are made, and put your ideas forward, asking the artist to reflect. Just working your own tree is nice, but it is a shame from having a big name artist nearby.
To me the aim of such workshops is NOT to leave with a perfectly groomed tree. I want to understand the way the artist thinks, and why certain choices are made. That is where the value is for me.
.
