Hi Nath
My training commenced on PA28 and on several occasions it was offline for repairs. On these occasions some lessons were in one of two 172s. At the time I felt it hindered my "feel" and progression, ie having straight and level session in pa28 and climbing and descending in a 172. With the majority of the training in the PA28, when I got to the airport and saw the 172 sitting there, I sighed and thought, not that cessna again!
But after a few flights it became apparent to me that experiencing differences between aircraft actually made me think more about my flying, and made me a better pilot, particularly reminding me why we do the things we do in flight.
For example, preflighting a different plane, different flap extension speeds (staggered in 172s), approach speeds, landing techniques, visibility high vs low wing, use of carb heat etc. After getting some consecutive lessons in the 172 I actuallly started to enjoy flying it.
On one circuits lesson, we actually had a flap failure in the 172 and my instructor sat grinning cheekily while I tried to work out why I wasn't slowing or descending on base quickly enough. He knew instantly but I was puzzled. As soon as he told me, I remembered not hearing the flap motors whirring away, and was cranky at myself for not noticing. In my defence, I was not used to such a noise as the piper's manual flaps just simply work.
Lets face it, archers and 172s are available everywhere to hire, and I think in the long run having flown both these types will help me. I recently went first solo at about 18 hrs, so didn't really hurt me in that department. Same goes for instructors, different instructor will give you a new perspective on your learning which can sometimes just make things click.
Go for it I say.
cheers
nev