I have also used this method several times and had no trouble with it. Mostly for baby quilts because they seem to end up about 45-48” wide, but also for a couple of larger quilts. I love that I can use a single backing fabric and have almost no waste/leftover fabric when I’m done.
It doesn’t cause any trouble on the long arm frame because the seam is distributed evenly across the width of the quilt, so there is no buildup of fabric on the take up rail because of the seam.
I use Pfaff machines with IDT, so I rarely pin, but diagonal backs are the biggest exception and I do pin them. I also starch before cutting. To help with the long cut I usually fold my fabric perpendicular to the diagonal fold at least once. It just helps manage the bulk.
@SuzSLO I love how you’ve matched the print on your truck fabric! I’ve been tempted to try that but never been brave enough. Maybe next time!
I can’t say enough good about this method and recommend it often. It saves me from having a bunch of long leftover strips in my scrap bin and let’s me use smaller cuts that I have in stash for quilt backs. The best place to test it out is on a baby quilt.
One of my diagonal backs is here, along with some links. The links may be inactive now.
Diagonal pieced back