I'm not a native speaker. A customer asked me whether a product would work for her, and I answered that it would work just fine. I was trying to say that the product would work perfectly well for her, but now I'm not sure if that was the meaning conveyed by that sentence. As far as I understand, just fine adds emphasis, is that correct? But I've found some dictionary and forum entries stating that the opposite was true.
As a native American English speaker, I think of the idiomatic adverb phrases just fine and perfectly well as near synonyms — both of which mean something like adequately or satisfactorily:
Why use a big word when a small one works just fine?
Why use a big word when a small one works perfectly well?
Why use a big word when a small one works adequately?
Why use a big word when a small one works satisfactorily?
These don't necessarily indicate that there is a shortage of excellence — only that attempts to exceed basic functionality are wasted.
I think what you might have wanted to say was:
This product will work perfectly for you.
But what you said works just fine; it conveys a sense like this:
You could buy that product for $100, or this product that does the exact same thing for half the cost.