I had used the Zagg Invisible Shield on my IP3 and really liked it
When I got the iP4 I ordered the OB and new Zaggs. I tried just the OB first but didn't really like the feel of the plastic shield. To me, it was not very sensitive to touch. I installed the Zagg and really did not like the way the OB shield interacted with the Zagg. So I removed the OB shield. I think I have the best of both worlds now.
I immediately did the same when I got my iP5.