The 20-20-20 refers to % weight. So, it's very high strength. I.e., you're getting more for your money.
The ratio is flat: 1-1-1. Some people grow with 1-1-1 all the way through. (I'm basically doing that with the MG Tomato.). There's nothing wrong with starting that way. But, eventually you'll want to experiment with raising N in veg, and PK in flower.
It doesn't matter what products you use to do that. You could use Jack's 20-20-20 as your base, and raise N using AK Fish (or MG All Purpose which is 3-1-2 ratio). That's why I encourage you to stay away from the boutique "lineups." Focus on the ratios. But, you don't have to get into that to start. Just use a 1-1-1 product and fine tune it later. I.e., you don't know what is better than 1-1-1 without doing it a time or two.
The only thing which is worth considering is whether you want to do organic or synthetic. If you are leaning toward organic, I would use a base like Grow More Sea Grow All Purpose (16-16-16). That's the same 1-1-1 ratio as Jack's. But, it has organic sources. From there you can increase N with AK Fish (another organic). And, raise PK in flower with the Flower & Bloom product (which, like All Purpose, contains organic sources).
If you want to do more organic growing, I don't think it makes sense to use Jack's. But, Jack's is a great product and I would use it before MiracleGro. (I'm just playing with MG because some people don't want to spend $30 on a tub of Jack's. $6 at Home Depot is preferable.
