I think I'm up to 5 alternatives, other than my main instructor (32 ish flat hours) in the PPL at various stages, and 1 extra for aeros at 8 hours (1/2 hour with the CFI on my 3rd flight). PPL & aeros instructor are one and the same.
The others have only acted as fill in when my main instructor is on hols, sick or if someone has beaten me to the booking sheets and he's totally booked up. I've only once managed to fly twice with an alternative instructor that I've flown with before...hence the total body count. Only equates to about 5 PPL hours & 1/2 hour of aeros though.
In the earlier days I was uncomfortable flying with other people (apprehensive) and would get confused by the different approaches.
I didn't feel that I knew much back then... so I didn't know any better, but I don't mind so much now - 'Cos
now I know I don't know much
.
If I'm told anything different by one of the others I either point out how I've been taught so the instructor can give their point of view on the alternative they're showing me, and/or bring it up with my main instuctor next time we fly so he can do the same.
The last guy I flew with for 45 mins before being sent off doing solo circuits, provoked a few differences which has encouraged discussion with my normal guy...All good and positive....I might add
.
So it's nice to keep the same instructor for consistancy in the early stages, but you can learn a lot and think about what you're doing more when you've got the basics sorted - more brain capacity available.