The battery holder worked great. I was glad that I ordered the exact parts defined in the instructions. The battery holder snapped into the frame (horizontally) which was nice. The vertical motion was suppressed with the recommended super glue and seems to be working great. I can imagine it being difficult to have it held strictly by the frame since all but the thin rim varies in height to accommodate the insertion of a battery and the spring to tension it.
It might be feasible to only lock it in place around the back rim, but that's a tight fit. However, having said that, it's not significantly different than the size of the frame's rim/ledge that snaps together nicely.
I do wish I'd used a thicker plastic so that I could have used countersunk holes for the three screws. The unit now stands on the three screw heads against the router bracket. That's actually not bad, but I'd love to have a flush surface.
Once again, I want to complement the models, design and blog post that made this a super easy project!