I did not know Hack Chinese, so I take notice of this, thank you.
When the DL course is well made (they are not all of the same quality) they accept different versions of the same sentences, admiting synonims and different syntactic variations as long as they are gramatically valid. This way it’s not simple root memorization.
That is something that, as far as I know, no other SRS does, and where the most added value can be found in DL. But I do not look for them too much either, I will be very happy to find other options of course. I will definitely that Hack Chinese.
Cheers,