It varies wildly by group and show. A lot of times, they aren't so good anyway.

In this case, it seems like the Crunchyroll scripts weren't that consistent, and the editing at Commie (based off of Crunchyroll scripts) was not particularly great for this show, though that's a subjective thing. Most of the Cthuko releases bother subtitling a lot of the Japanese text that flies by on the screen (some of which actually add some value to the show like what those CROWDS and social media postings are saying), and I would say the main subtitles are a bit better as well.

For what it's worth, Cthuko announced that they were doing BDs for the show too, so there's some point to getting the releases done. It needs to be translated anyway for that.

1. Sub-Groups: There are types of groups: Speed-subs, Archival-subs, BD only-release subs.  The BD-only release groups almost always use R1 subs from the BD or existing fansub scripts. The question is whether or how much they polish things up.  Such groups sometimes/mostly claim no translation skills.
2. Speed-Subs (release within hours of broadcast): There are two types of Speed-subs: CR-Mod and Original translations.  If there is a CR script, most groups think it's a better use of time to modify an existing script than to start over from scratch.  gg-subs might be the only speed-sub left that only does original translations (sometimes, very original).  Commie is probably a good example of current practices: A couple of years ago they would do 3 - 5 shows per season, all original translations.  Last summer they released 19 shows, 17 of which were CR-Mods.
3. Branding Consistency:  This is your real question.  It's surprising how we expect/hope for branding consistency given how fansubs come, go, and operate.  Instead, you mostly have to evaluate projects one by one.  Here's a place that does some of that:

http://www.crymore.net/

4. Oversubbing: It can't be helped.  People fansub the shows they want to watch.