I like the shape of yours better but also couldn't decide where to put them because of only 3 fins. The ones I put on are 1/4 inch half round polished stainless steel and I was able to put four on so it matched up with the four vents we have on our cars.THAT'S FUNNY, I was thinking of the very thing this last month and ordered these 3 fin stick-ons.
They came yesterday and haven't had a chance to see whether to mount them High, middle or low in the vent.
The angle is just about perfect to match
Obviously this pictured one is for the passenger side
Love to see what you decide, please post pics