My vote is for no *open* hands on displays
except to interact with the old software
through faked or "new" keyboards, etc.
An exception is to allow experienced users
to do hands on at special events, or with
a tourguide's permission.
The example I have is Science Museum, Boston.
The computer display had the KB set up with a
1/2" plexiglass shield through which the visitor
had to type down through to reach the keycaps.
Somebody still managed to pry off many of the
caps. Think Zoo, unfortunately.
John A.