very well informed opinion sweet.i.f 
I’ve tried cue cards on multiple occassions, but they’re not for me. I stick to writing my summaries and key take-aways on normal lined paper and try to review it twice after writing the stuff down.
Group studying on the other hand does wonders for me when I do it right. There’s a process behind it…
i) you need to have at least gone over the material on your own… sometimes when group members haven’t done this, we have a timeout for reviewing the next couple of chapters before meeting up again and discussing.
ii) the group discussion needs to be focused:
One way to do this is to ask different group members to prepare challenging questions on different chapters/topics. This does two things: One, it gets everyone motivated to prepare questions, and while doing so, they study those chapters really well. Second, for the others who’re going to respond to questions, the challenging questions will probably make them pay more attention to detail that they might have missed.
The other method for achieving focus is to allocate tasks to group members to prepare summaries of specific chapters and provide them to the rest of the group. Again, the person preparing the summaries gets well versed with the material in those chapters, while others avail the opportunity to complement their own review with the summaries that were prepared for them. Also, the summaries can be used as wireframe to discuss more details about the topic. Concept maps/Mind maps can also be used in place of summaries or in addition to them to help drive the discussion process further.
The point about focus in group discussions is where I think people go wrong… they come together without an agenda, and end up wasting time in chit-chat and/or doing only a cursory review.