I agree, the FireFly tastes better. In the end the Solo has a metal oven with a glass path, the FireFly has a glass bowl and lid, then a stainless steel path. Not very different. And I don't think we can assign taste properties to materials so easily, it's more in the overall design. We're not the only two people to think the FireFly rules on flavor.
The vapor coming off the FireFly convection chamber is cooled by the SS pathway in the lid, that could be a factor, it's a clever design, while the Solo hits right up the tube. I still suspect the more gradual heating on the FF, and its lower default temp plays a big role. If the 2014 Solo runs hotter than originally, then if it were run maybe at 2 initially, and the vapor cooled with a longer pathway, it would come even closer. At 3 I was done, judging by the color, taste and texture, I didn't find I wanted anything remaining in that ABV, it's just heavy head terpene stuff. I'm not complaining at all, the Solo is a lovely unit, and more versatile in some ways, but the FireFly deserves its laurels where it shines.