I live in Arizona, and have a 20-minute walk into work every morning.  I use this umbrella every day and it does its job well.  It really does feel cooler when I walk under it -- this can make the walk in to work bearable when it's 100+ outside (whereas my regular rain umbrella does not).  And more importantly, it seems to be very effective at shielding my skin from the sun.  I'm fair-skinned and paranoid about cancer, and I feel very protected when I walk under my Coolibar.

Two caveats.  (1) This umbrella is thick and bulky and harder to fold up than a normal umbrella -- you kind of have to muscle it.  It comes in a little sheath and I've never once been able to get mine back into the sheath.  (2) It only lasts so long.  My first one lasted about two years of consistent but gentle use before starting to fall apart; I managed to get a third, limping year out of it.  I've just received my second one -- so, it was worth ordering again, but it would be nice if it lasted longer.