Dear sweetpetal,
The short answer is : "yes, it is edible, but ..."
To elaborate a little, there is no doubt about the palability of Fortunella japonica. Every Fortunella species, except maybe Fortunella hindsii, is edible.
Fortunella japonica is very edible. No problem.
However, I would advise caution about eating any existing fruit on the tree. I have heard that producers that heavily use pesticides and insecticide just don't bother to warn about the temporary inebility of the fruit, and simply label the whole plant as "inedible", which in fact is not true, as it is just a temporary statement.
Conclusion : don't take the chance to eat any existing fruit on that tree, just in case. However, the next crop will be 100% fine
Etto
