Concentrates are often made at 68 brix, so it's diluted down to a desired level, typically 21 to 25 brix. I'd lean towards the vendor's recommendation, as for the reputable ones, the acid is more likely to be balanced at that level of dilution.
However,
@Jim Welch's tale is a good caution to pay attention, use your hydrometer, and think your way through what the result will be.
To answer the question I believe you want answered, the ABV of a wine is directly dependent on the starting sugar, regardless if it's measured by SG or brix. In Jim's situation, 28 brix produces 16-17% ABV, depending on which formula you use (all ABV formulas are an approximation).
If you start with the SG between 1.085 and 1.100, you will produce a table wine strength. For light fruit wines I tend towards the bottom of that scale, for whites and quicker drinking reds, the middle. For heavy reds I'm at the top of the scale, maybe a bit higher. This is driven by the relative body of the wine.
It's hard to provide an exact answer, as there are many variables, including
your taste in wine.