Dave Doe wrote:

I think it's fine - once you have your PPL! ie I don't think it's a
good idea to mix plane types while a student pilot.

Fly one airplane, and only the one you're currently flying, at a time.

While attending a Part 141 school, I swapped between (3) differently
equipped PA28's with AI's calibrated in knots. At 20 hours, I changed
to a BE23 with an AI in MPH, and took my check ride @ 47 hours.

I was required to give a ~30 minute presentation to each instructor on
the systems and flying (V speeds, emergency procedures, etc...)
differences, using the POH's as visual aids. None of the instructors
had previously flown any Beech 23 family aircraft. I made laminated
V-speed and extra checklists that were offered to each instructor and
the DE. In hindsight, I think the extra homework was beneficial, and an
excellent experience. Both aircraft became that much more detailed in
my mind.

A great example learned while actually flying involved stalls. Using
the stall recovery technique for the Warrior on the Sundowner resulted
in an unwanted pitch down attitude, while gently relaxing the elevator
pressure worked perfectly. The Sundowner also needed slightly different
inputs to slip, when compared to the Piper.

I believe that I was a much better pilot when the DE arrived for the PPL
ride, because I felt like I _really _ knew the aircraft, in addition to
being able to execute maneuvers.

All in all, I think changing aircraft can actually be good, if the
student is willing and able to put in the proper effort.