Yes, they are very easy to use. You just start at one end of the scarf, and push (feed) the end of the blocking wire through the end stitches all the way along. If you have worked 'edge stitches' on your scarf (or really, any project that has a long straightaway edge, like the sides of a sweater) then you just push the wire through the purl bumps. (see photo)
But if you've worked, let's say, slipped edge stitches, then just feed your wire through the 2nd stitch in from the end. As long as it is consistent, and when you pull out the width of your scarf, it is even tension. You wouldn't feed your wire through the 2nd stitch for a few rows, then divert to the 3rd stitch, then back to the 2nd stitches. Keep a straight line.
I feed the wire through side A...get side A anchored into the blocking tile, then feed the wire through side B...then PULL side B away from side A to bring the scarf to the desired appearance and width. I place pins on side B directly across from side A. They face each other to begin. I might tinker around with pin placement before I leave it to dry. Then I just keep on til I like what I see in the scarf.
When the scarf is dry, just pluck out the pins that hold the wires apart, and then pull out the wires! voila!
See on the left side, I pushed the wire through the 2nd stitches.
The 2nd stitches were more amendable to the wire.
But on the right side, I pushed the wire through the purl bump on the very edge.
At the cast on edge, you can see that I pushed the wire through the knit stitches of row 1. It worked great.
Here is the scarf, with that end all done!