You have to create an account to get at the OS images, but they don't require any proof of purchase to download things. The boards I have came with an Ubuntu image, but I've downloaded updated images from their site and flashed them. They also have RHEL, and some containers that are supposed to help you build your own images.
They're expensive. I think the high-end BF2 cards I use at work (2x100Gbps Eth/IB) were about $2.2k, and 25Gb/s go for $1.1k. Nvidia's store says the msrp is more like $3.5k. Make sure you read the power/cooling requirements. I wouldn't use these in something that isn't rack mounted and can push a lot of air over them.
https://www.flightradar24.com/blog/tracking-flights-with-our...