AOB9...
RAF "practice", which I assume was dervied from some study/experience, is for a student to have a Primary and a Secondary instructor. If required you could fly with any instructor, but best efforts were made at the planning stage to fly with one of these 2.
In the event of encountering difficulties with progress, one of the "tools" considered early on was to swap your main instructor to see if that helped.
To me 6 in 8 is far too much change, especially at the early stages...
NoD