On fuel mileage, my Ursa has Yakima rails (with an old school wind deflector) and a 100 watt solar panel up there. I'm lifted on 33"s with a 2.5 AEV dual sport setup. 6 speed Jeep got 16.5 on a recent 5k mile trip out west. Mileage suffers most at interstate speed, went up close to 20 everywhere but the interstate, pretty much the exact same as my JKU without the Ursa on top.
Also, I'd like to give John at Ursa some credit. He's a small shop and I've patiently dealt with many like him in this hobby. I heard his customer service was sometimes lacking before I got my Ursa. I bought mine used but talked to him at length about a new one before I found it AND he's helped me with a couple of questions since I bought it, even though I didn't buy a new one from him. He is a spectacular guy IMO. He has always answered the phone or gotten back to me within hours. I'm not questioning any one else's experience, just sharing mine.