tl;dr:
- Better UI/UX
- Better privacy controls
- Better control over what permissions group moderators can be given
- Forum staff can manage social groups
- Main group page is customisable by admins via the Widget system
- Main group page displays more info
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Up until last month, the biggest difference would be XenForo 2.3 support
Other than that, I would say the UI/UX. One of the main things I pride myself on is making addons that look like they could be official XenForo add-ons - that is to say, they fit seamlessly into the native UI. Navigating Snog's addon when I was creating an importer was challenging for me. I would have to imagine that the multiple non-standard UI features shown in their screenshots would not play well with more advanced 3rd party styles, though I cannot say that for a fact.
Other than that, an important difference is how you navigate groups. Snog's addon uses categories, whereas I use tags. In my opinion, tags are superior to categories because they're the equivalent of adding a group to multiple categories at once.
Admittedly,
searching for groups via tags can be improved in my add-on (and I believe there's an open ticket for that from the person who is funding most of the feature updates, on the back burner just now). Ideally, it would be possible to combine tags to find only groups matching all tags, similar to how you would filter, for example. a manga database.
Another important difference is the back-end that's being used to store group discussions. Snog's, as well as truonglv's, uses forums and threads as their back-end. This has pros and cons.
A pro would be that you don't need to reinvent the wheel; XenForo has already done the heavy lifting when it comes to how to post threads and posts. Add-ons that deal with threads and posts will likely work out of the box too.
A con would be the fact that XenForo's permission system currently does not like it very much when you have a large number of forums (nodes) created.
When I experimented with back-end storage during development, creating only 100 social groups already slowed down the creation of future social groups to an absolute crawl, forcing users to sit through a minute-long "Rebuilding permissions..." pop-up, like the one you would see if you added a new node or changed a node's permissions on your site just now.
In other words, it straight up does not scale very well. Even if you bypass XenForo's permission system entirely for social group nodes, you'd still run into the same problem the next time you wanted to make a change to nodes in the AdminCP, forcing you to wait for minutes per change.
Other than that, it also pollutes the node list when, for example, moving threads, forcing you to scroll past potentially hundreds of nodes.
Furthermore, when using nodes as the back-end, disabling or uninstalling the addon would render all the social group content visible to normal members, if you don't also apply permissions to all the social group nodes manually before doing so. Of course, with my back-end, uninstalling the addon will simply delete all the data, so that could be seen as a downside of my approach.