Here are two pics of Carina taken with 80ED with/without Hutech DGL focal reducer/field flattener. Both images reduced in size only (unprocessed) from JPG.
Camera Canon 5DH
With FR
http://users.bigpond.net.au/avandonk/80ED+FR_2.jpg
Without FR
http://users.bigpond.net.au/avandonk/80ED_2.jpg
You be the judge how well it works.
Bert