Question on Tefillin Dakkot

I buying Tefillin for the first time. I have been researching the options and have a question about Tefillin Dakkot. As price is an issue, I have been looking at buying Tefillin Dakkot which are both less expensive and which I aesthetically like. I have read the Chabad site on why Tefellin Gassot are preferred, and have read that Tefillin Dakkot used to be the norm before more modern production techniques and that they remain a Kosher option.

For those familiar, what would be the argument against purchasing Tefillin Dakkot?