Yes, they are that good. The 4 stars I have given is in comparison to Elixir, EXL and other premium brands, not taking the price into account. Considering the price it's a clear 6-star (if that was possible). At this price point its incredible what you get.
When do or don't I use these strings? For recording I use premium strings but for everyday use these are fantastic. The strings on my kids guitars last longer and I use them right now on one of my vintage acoustics.
I have not yet made an A/B-recording with these strings and premium strings, but I bet that these will sound at least 90% as good. In a mix I doubt you will hear any difference.
I will always keep a stash of these at home.