Pros and cons of publishing in a mega journal?
In my opinion there are almost no disadvantages here compared to similar well received and indexed journals.

The usual argument would be that people who read this journal aren't from this field, so it might not be as interesting to them and people within that field might rather read the specialized journals and might miss it so you get less exposure.

I think this might have been true several years ago or even more some 30+ years ago. However, today there are so many publications every week, even within specialized subfields, that it's basically impossible to read all the journals relevant to your field or even just the biggest ones. Most people I know (including leading researchers) have given up on reading certain journals. What people do instead is creating alerts for certain subjects and frequently share intersting new articles which means as long as the journal falls into the index they use they will find it anyways.