There are slightly different specifications to them. The model with out the Q in is rated at a higher spike current (36,000 vs 30,000) and it appears to be packaged with a cable. I'm not sure the other one is not, but the belkin site does not list it as part of the package (though it doesn't list anything for what's in the box)

The other difference is the one without the Q is listed as

Comes with Lifetime Product and $75,000 Connected Equipment Warranties

while the one with the Q simply says

Comes with a lifetime product warranty