I’m wary about this mechanic, and not sure I’d trust him with my bike:
1. As others have said, the new 7000/8000/9000 shimano absolutely does not need an inline adjuster.
2. Even on older stuff, while it was certainly *helpful* to have the adjuster, it wasn’t absolutely necessary. I set up 5800 on a bike without an inline adjuster, and had zero problems with it for thousands of miles.
My own experience with a R8000 FD: I followed the Shimano instructions VERY closely and lined up the lines just like they said, and I haven’t had to touch it in over 1000 miles. The trim works perfectly (all 22 gears accessible).