Four-Thirds lens on m43 ?

So I am new to the m43 world. Currently have a lot of Canon big L glass. Want something smaller but great quality for family stuff.

I see Panasonic makes a Leica Elmar 14-50 for four-thirds and an adapter for m43.
Is there any focus, exposure, or other issue using that lens on a P3 or GX1 ?
Does it focus almost as fast or ... ?
Other than size of course.
Thanks
Barry