I had another company install roof ductwork for me in 2018 and I was quite disappointed with it.
Nichols replaced 50% of it this year (2019) on my request. The quality of Nichols work on rooftop ductwork is dramatically superior to anything else I have seen. Their structures are straight, aligned and very neat. The ducting they replaced had been out of line, twisted and dented.
Even the finish of the ductwork by Nichols is excellent.
I had them 'double-skin' my ducting with an additional layer of insulation around the ducts, and then a metal overskin. No other company I had bought in to give me a proposal suggested that, and living in Tucson, it is desirable to reduce air conditioning losses as the duct passes over the roof and into the living space. The additional skin reduces losses by about 40% over a single skin duct. The additional cost for the second layer was very reasonable.
We were renovating our property, and as is typical, we had some hiccups along the way. Where it impacted Nichols they were always very patient and accommodating. I would not hesitate to use them again.