After you learn material it’s feeds you “reviews” on a set schedule to beat the variation(s) in your head.
Personally it’s been a game changer.
The instructors also explain literally every move with many variations going 10 to 15+ moves deep covering the main ideas and strategy with each line. For me, that’s something I always struggled with. Knowing the first couple moves of an opening and saying now what?
I may sound like a a Chessable rep but whatever. I wish I found out about it earlier when I began studying.
#SmashEm
To put it mildly, the Chessable move trainer sucks badly, especially when the course is not made properly (which is about 90% of the offered courses).
A single move (no alternatives, they aren't even mentioned) is shoved down your throat until you repat it by yourself, like a parrot. Like that, usually with no explanations why this move is preferrable to move XYZ, and offering tips for understanding why you play this, or that.
Studying chessable courses will probably make you learn many opening moves, but certainly enough not playing better chess.
Usefulness? Somewhere around zero.
You can study wikipedia articles, read books, watch videos online, buy courses in the webshop https://shop.chess.com. There's lots of things that you can do to help you learn openings.