We had our gutters replaced last year and had gutter guards (unsure of brand name) installed.  They are perforated sheet metal that fits into the gutter.

They do as promised, they keep the leaves out.   However they do not prevent cleaning the gutters.  All the little stems on the maple seeds get stuck in the holes. Stuff builds up and the gutters overflow.

There was a company at the Louisville farm show selling a different kind of guard, but I can't recall the brand name. They were somewhat like these

there was nothing to catch things.  I don't think this was it, but they were similar. The one pictured has a screen over a support piece.  The theory is water runs through the screen but material slides off.  Can't be any worse than my perforated sheet metal crud catchers.

You might find this article interesting http://davidbaldwin.co/gutter-cover-reviews/