Just had five of them planted on a roof a couple months back- custom heat recovery ventilators in the 5,000cfm to 10,000 cfm range. The only issue I had was that we specified coated acoustic insulation behind 26 ga. perforated sheet metal liners, and they used Tyvek House Wrap in behind the perforated sheet metal on the liner insulation. The Tyvek meets the smoke and flame rating for "plenum rated material", but still....
I know of a few more that I've seen that have been running for 2-5 years and no issues I've noted that would cause me any heartburn.