My experience is hugely positive. The biggest downside is time taken to sentence mine. This can be brought down to 0 with new technology.
I used to first get all the sentences in an anime episode into sentence cards in Anki, and then use an add-on called Morphman to keep track of my known words AND automatically reschedule my Anki cards so that the i+1 cards would automatically show up for reviews first. (If I ever ran out of i+1 sentences, I could just repeat and get more sentences.)
But now this process is even more seamless with a paid extension called Migaku (I promise I’m not sponsored, I just love this product so much).
Like Morphman, it also keeps track of your words, and you can use it to automatically stop a sentence mid-show if it is a 1T sentence AND the unknown word is within a certain frequency threshold (big improvement over Morphman, which would often lead you to study obscure words…) And it can be used to show two subtitles at once on Netflix.
Not only that, but with Migaku, you can simply export all the 1T sentences (whose words are within your frequency threshold) of the entire episode in bulk - no need to export the entire show before rescheduling. The process is way more seamless.
To be honest, I don’t even make sentence cards on Anki anymore, because with Migaku, I can see in underlines the status of the words no matter what site I am using. There are three statuses: green (known), yellow (learning), and red (unknown).
My new system is to mark as learning (yellow) those red words that I searched up for the first time (and that I think I could remember next time), as green those yellow words that I understood at least one day later without looking it up, and back to yellow those green words that I forgot. This results in natural immersion for me, always using new sentences rather than hammering down the same sentences.
But I must say that learning words in context is a huge positive, and sentence mining is a great tool. Also, bulk exporting mined sentences and studying them leads to a more consistent study schedule than simply “keep immersing” and you can set particular goal amounts of new words more easily this way.
So the pro of my new system is that it’s more effective than my already pretty effective old sentence mining methods, but the pro of my old ways is that it led to more structured studying (e.g.: learn 20 new words in context per day.)