I doubt the quality of the DVD will be very much higher than the YT clips. It will have been shot on NTSC (American standard) standard definition video, so by the time it gets to a UK screen it's likely to be a bit shabby.
There is a link to buy it direct from the states, but it doesn't state whether it's a worldwide DVD format or not. Make sure you check before buying that it will play on your player, if it's region encoded it may well not.
I wonder how much more revenue people would get from these sort of niche videos if they just sold them as downloads in a universal format at more affordable prices ? £40 seems rather a lot for this one when there's so much decent free content on YT.