I played this with a group and it went great! The session length was 4 hours and it was a bit rushed, so I reccomend playing this trought two 3 hour sessions.
I think this module is structured in an interesting way: the intended course of action is somewhat linnear but it's not directly stated, it's pieced trought clues in room descriptions so it takes a bit of careful study from the GM to understand how the adventure is meant to be played; for example, it's intended that the party only learns about the ori magi's shadows by reading the book in Capiphrel's Study.
The rooms are filled with clues like that, so while the party can freely move trough the dungeon, it's up to them to investigate and gather clues to learn the right course of action. In this sense, this adventure is similar to an escape room.
In any moment the party can fight the NPCs or even the final bad guy, but they regenerate after 10 minutes, so that gives them an extra layer of discovery and experimentation.
Still, for my game I made the paper flower Ori Magi to be able to speak and info dump to the party some of the details, and later I spelled out the info they had gathered, wich made things a bit faster (it's always ok to spell out previous information, it's an OSR principle).
I think this adventure can be played in a more methodical way trought many sessions, letting the party gather the clues and fight the enemies many times until they learn how to defeat Capriphel.
Overall, I think this module is cleverly and densely designed and can be a lot of fun to be play. It's some of the best Mausritter content I've played and it has extremely original ideas I've never seen before in an adventure.