Testing new anti-suspension system (thanks <redacted>)

\youremailaddress@somewebsite.com\

maybe formatting it as inline code would help? <youremailaddress@somewebsite.com>

Super short version, yes, there's a reason- but the reason has been <redacted>. :P

Short version, yes, it could have been written either way, but yes, there's also a reason for the square brackets. The distinction in the usage is that I was attempting to express a different tone with the text than parentheses would have given it.

Long version:

As I noted, parentheses (round brackets) are meant to be read as part of the sentence, and are used by the narrator/speaker to include a tangential subpoint (that is, an aside), either to offer clarification or add additional detail to the overall discussion. They're a pretty strong element of conversational writing, as it is pretty natural for conversational sentence flow to include such usage:

I hear that John (along with his family) really enjoyed his vacation.
After 2 years of waiting on cg to update the FAQ, the userbase was fed up with cg's updating habits (or, rather, lack of such).

As with the four examples above, they add information that, while perhaps interesting, isn't critical to the core point of the sentence. Instead, they're meant to add tone, flavor, or clarification to the topic in question- in doing so, they can change the overall impression of the sentence (as with that last example, giving it a slightly more negative indication).

Square brackets are meant to add additional information or edits to a sentence, but aren't meant to be read from the perspective of the narrator/speaker. Where parentheses are a common element in conversational writing, square brackets are more a component of scholastic writing or [edited] quotations. Aside from indicating edits, they're meant to provide outside clarification where meaning may not be intuitive- thus, where rounded brackets indicate a continuation of personal perspective, square brackets indicate outside perspective (or reference to such).

In other words, either round or square brackets would have worked in the paragraph you quoted, but the difference is one of intent- had I included it in parentheses, it'd have shown I'd intended it to be a part of the sentence flow, and as an element in further expressing the point the sentence was covering.
More straightforwardly put, parentheses would have indicated I was emphasizing the contrast in question as being a relevant part of the sentence, due to my stressing the extra mention within the sentence flow itself. Aside from the shift in tone, this could also imply that other options (aside from internalized redactions and 'actual' redactions) are part of the sentence's considerations, and that I'm stressing the specific alternative so as to distinguish it from those. Consider (along with his family), above, as a similar arrangement- that aside implied other options had been available to John (primarily, the option of vacationing alone), and the inclusion of the aside served to stress the specific approach that was used.

Square brackets, however, make it clear that I'm just offering outside clarification of what the preceding elements were intended to convey (and that no change in the sentence's impressions is intended). As my intent wasn't clarification of topic, but clarification of what the preceding element was intended to reference, that's a more appropriate formatting for me to have used there- especially as I'd never have included the clarification had I been speaking the sentence out loud to someone, which is also a clear indication that it's an outside clarification, rather than a conversational one.

tl;dr: You should use round brackets to clarify the topic and elements related to it, and square brackets to clarify grammar and elements related to presentation.

As a final note, had I intended it to flow as part of the sentence, I'd actually have formatted it as such:

As no actual redactions are occurring, angle brackets theoretically are actually the more accurate grammatical formatting, as they better indicate the perspective of the redactions as being internalized to Mully, rather than being redactions which are actually occurring due to outside interference.

(As this formatting avoids any confusions of intent that making an aside of the clarification may cause.)

In the end, the nuance is mostly in how I intended to convey the matter (that is, in downplaying the need to put meaningful consideration toward the bracketed material). You could just as easily have presented it with parentheses, and it may have been the more accurate option for how you would have expressed the matter. As both forms of brackets are intended to offer clarification of some sort, they do sometimes overlap in ways that make choosing between their usage more a matter of personal perspective than straightforward grammatical consideration (at least, so far as their usage in casual written environments such as those found on forums goes).