To be fair, it has been a long time of the decline and increased monetization.

I remember using it at a time where gems had only cosmetic use or you could freeze your streak.

I did not use it for a couple years and came back to gems being used for a whole lot more, a few free exercises and then it cost gems. Getting the final, I think gold, level of each exercise cost like 100 gems a try, no mistakes allowed.

The only reason I still kept using it was that in the early years I amassed 10000+ gems, so I was slowly using those up. Once that was over I stopped, unusable without paying and even then it does not provide more than vocabulary practise.