I not only changed my FI but also my FTO at 7 hours as I was not progressing.
New school was a revelation-I made good progress.Up to and a little beyond solo I had the same FI ( although I soloed with another FI as my 'regular' was still restricted).For the last 15hrs or so I had one or two different FI's due to no other reason than availability and felt this was beneficial.
To summarise the above waffle:If you are happy with this person then stick with them for the majority of your training but a couple of lessons with someone else later on may be of benefit. ( this will probably happen anyway if you at a place with several instructors).
Good luck with your training
MM