I use Jacks pretty much exclusively.
20-20-20 is really great. I use it pretty much exclusively, and only run into issues with longer flowering strains. I don't know what you are using as a medium, but if I have a 10 week or longer strain, in fox farms Happy Frog, I run into a calcium problem.
I just used up the last of my 20-10-20 Jack's Citrus. Generally I was using this towards the end of flowering as it contains magnesium.
One thing to be aware of, and I've noticed it on a couple of strains that you want to definitely ramp down fertilizing towards the end as its possible to have a strain re-flower.
Jacks is really solid. Only other thing I use is a Potassium Silicate. Seem to get stronger stems when using it v. Not using it. I do amend my medium with calcium to avoid having to use anything else for my longer flowering strains.
I honestly couldn't be happier with the product and the value I get out of it. If you have any questions I'd be happy to try to answer them.