That looks like a good deal for a non mechanical person wanting to convert. Good chainline adjustability and no worries on getting the perfect chain tension through sprocket math.
Me, I would drill the cassette rivets to free up a selection of sprockets and 50% of the spacers required. Then I would go to a hardware store and buy 2" of abs plumbing pipe. (Any naysayers, check out what the spacers in a cassette are made of.)
Now I would have 3 front and 8 or 9 rear sprockets to play with. With this I would play with until I had a good gear ratio and perfect tension so I would not need a tensioner.
After I had the chain line and sprocket choice made, I would buy the one bmx sprocket I want.
Sound easy? It is.