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Contrary to what it says, I don't believe it conforms to the regs. There's nothing crimped, soldered, or brazed about the connection (at least, as far as I can see in the picture).
It looks to me like someone just misunderstood that screwed connections are not permitted. Screwed connection would however be a damn sight more reliable. You can't get a gas-tight (corrosion resistant) contact using a spring terminal, and you definitely don't want an inaccessible spring terminal.
The most accepted method is to use crimps. I have used a regular screw terminal junction box and then soldered the terminals too, but this is only suitable if you are good and competent at soldering.