pros and cons of risers.

Probably unmeasurable impact on gas mileage. The real decrease in gas mileage happens when you hook up the Pod. My dealer said the risers were worth their weight in gold. He was only half right. They are worth TWICE their weight in gold.  

I never noticed a significant change in gas mileage between with and without Risers. I had my trailer a year before I put on the risers.  

Just a thought here.  Everyone agrees (so it seems including myself) that MPG seems to fall in about half (maybe not quite half but close) when pulling the pod.  I wonder if it would be worth the investment to attach an air deflector on the TV to shoot the resistance up and over the pod.  I'm not even sure if those deflectors (hope everyone knows what I mean by that) even really work or make much of a difference, just a fleeting thought.. 

On a tractor/trailer the airshield on the cab roof and the fairings on the side of the cab do work very well if they are 18 inches from the trailer but not over 30 inches, after that they start to loose their effectiveness. The same holds true with a TV and the POD, you really need a set of fairings that extend a little ways from the back of your TV to start to see any improvement in MPG. Those that have put kayaks on the roof of their TV's have reported better MPG as the kayaks are much like the airshield on a big rig.
I would not think that risers would have much a difference in MPG. Putting flexible side skirts on your TV and the POD may help some, just like on the race cars.   Goose

I got the best mileage ever on the last trip and it was the first since putting on the risers.  The only thing that helps is keeping the speed to about 55-60.  I loose 5MPG (20 to 15).  If I go 70-75 I loose half (20-10).