Q: What is difference between using brackets and two hyphens?
bla bla (explanation) bla bla
bla bla - explanation - bla bla
A: This is discussed in the Chicago Manual of Style and similar publications. (NB: two hyphens are a typewriter-oriented convention used also by computers because they adopted the typewriter keyboard, with a hyphen (en dash) but no em dash as used by typesetters. This is also discussed in comprehensive style manuals.)
The advantage of such investigation is that, when we reach a decision differing from the style manual, we can offer our factual reasons and propose its debate in NGs like this.
By the way, a hyphen is not an en dash. See the Merriam-Webster Standard American Style Manual for a full discussion of the dash in all its lengths.