I can forgive the somewhat limited user interface for setting these up that is in the stock add-on, but the lack of automatic syncing of rules to all computers with the same Firefox account is really frustrating to deal with.
Putting in the effort to get them all set up nicely and then having them either blown away (I think this happened once...) or needing to get that over to another computer has made me limit my use to fewer containers than I probably would otherwise use.
That particular bug (having my container setup get blown away) has happened to me several times along with other bugs like not properly restoring tabs in the designated container when you restart FF to apply an update.
Bugs like that would be forgivable if they'd at least provide a way to export/import setups.
There is a plugin that will sync the actual containers, but it doesn't sync your rules you setup to always open site X in your personal container, etc.
Without that, its useless to me. There is a bugzilla [0] for it, and 3 years ago, it was said they were going to look more into it, and nothing really since.. Its frustrating.
Predictably, synchronizing data is complicated, so it's taking a while and we're trying to do it in a way that doesn't destroy any existing data. So we'll be doing some heavy internal testing on it before we release it.
Putting in the effort to get them all set up nicely and then having them either blown away (I think this happened once...) or needing to get that over to another computer has made me limit my use to fewer containers than I probably would otherwise use.