I notice that there are Ivoprop makes an in flight adjustable
propeller suitable for a an o-200 engine.

I understand that putting this prop on my C-150 is illegal. But
suppose ...

Suppose I put this prop on my Cessna 150. It only weighs 9.5 pounds,
as compared to the Sensenich weight of 24 pounds. So I save 14.5
pounds.

Can anyone guess how this would effect my performance? How much
better climb and how much better cruise?

-Just curious

See http://www.ivoprop.com/inflightultralightmodel.htm
And http://www2.sensenich.com/misc/c150.htm