[Avodah] Tefillin with plomba

[Simon Montagu]

I saw on a blog a picture of tefillin with a "plomba" like a kosher
chicken, stamped on one side "Kasher" and on the other "Harabbanut
Harashit TA-Yafo".

I have never seen this before, either in pictures or in real life, but
then I have only ever bought two pairs of new tefillin in my life. Is
this common practice? Is one expected to remove the plomba before use?
The blogger thought it wouldn't be hatzitza, but I don't see why not,
since at least in the pictures the wire that the plomba is attached to
comes out under the corner of the bayit, though it would presumably be
possible to attach them so that it didn't.