Their full strength mix is
Part A: 3.79g
Epsom: 0.99g
Part B: 2.52g
I don't run full strength, I started with autos at 80% strength, which funnily enough is actually the 3/2/1 formula: 3gA, 2gB, 1gEpsom. It works pretty well. I mix 4 gallons at a time so the nutrient amounts guarantee a proper blend of the powder components. A trick I learned from MoG mixing his megacrop. You can up/down the strength by either reducing the amounts in % ratio or just multiply by one less. Example: 3/2/1 x 4 for the 4 gallons and its 12/8/4g each OR just do x3 and use 9/6/3 into 4 gallons. I do bump the Epsom a touch higher for coco. Usually 1.3g/gal insted of just the 1g/gal.
The only thing I add is a liquid silica. I use that as a pH buffer in RO. The Jacks line tends to be pretty acidic. Mixing up just the plain nutrients and the pH ends up around 5.5-ish or lower. It took a bit of test and tune but I can pretty much hit my target pH by adjusting the amount of silica. It holds very very stable for several days, both pH and strength. I bought their full kit, even though I know it was probably far overpriced, especially for epsom salt. Ah the price of convenience!
This one:
www.jacksnutrients.com
I do use the clone/seedling product when starting new seeds. I also use the bloom booster during the transition period to flowering. Then it just switches back to the normal 80% strength until the end. I did use the finish on my last photperiod plant and it worked quite well.
There are several far better growers than I using the line. I have only used it in coco so far. Quite easy to simply flush if I see a mistake developing and I am far from good enough to decipher nutrient issues.
You do need to mix in the correct order: A/Epsom/B, or it will get cloudy. Plenty of videos and help/guides on their website as well. I like to mix mine and let it sit for ~20min just to make sure the pH and ppm settle and are where I want them. The powder can take a little stirring to dissolve fully but it does quite easily. Ok that's probably enough of a book eh?
Other growers I can think of who use Jacks:
@Cave Dirt Cody ,
@Cerebral Goo , and surprise!
@Son of Hobbes said it worked very well in a commercial grow.
EDIT: The Twenty20 SparkleFace photo grow in my signature was a full Jacks run. Turned out beautifully. Not a crispy/yellowed/malformed leaf on the whole thing.