Plugin to "check/uncheck" all matrix blocks while editing entries?
There's a related feature request for this: "Expand/collapse all" UI for Matrix fields

In that feature request, Brandon Kelly explains how this is already supported (it works very well):


  There is a way to achieve this: Check one of the blocks, then hit
  Command + A to select all blocks. Then click the option button on any
  of the expanded blocks and click "Collapse" to collapse all blocks,
  and vise-versa to expand all blocks.