It's been fantastic reading all about puppies trying with Burns.
Daisy is really happy on it, but I did want to say that, contrary to what some have said, she doesn't have a "smell" with it at all. Perhaps it's what you are mixing with the Burns?
Some days she just has Burns (and treats when training), but other days I add a small amount - dessert spoon perhaps ? - of cooked chicken breast, or tuna, or scrambled egg, or pasta - by way of a change, with the Burns. She loves this!
But she's never had a "smell", fishy or otherwise. I find the tuna does loosen her tummy a bit, so we are careful with that, but even so, no "smell". Have never used Nature Diet, so can't offer opinion as to whether that's doing it or not.
I am so pleased I switched her to Burns, and the company itself has such a good customer service that it makes it a pleasure to deal with them.