I submitted a manuscript to a journal for non-open-access publication and the editor came back and said that they want to publish the article as open-access (same journal) and waive the fee for this.
As not to be too broad, what implications does this have for my paper? Is it generally viewed positively to have OA publications? Really, in the end, I am trying to look at the pros/cons of saying yes/no to this.
It is still an open question whether open access actually leads to more citations or not. This is at least partly because the models and players in OA are still rapidly shifting, especially with the rapidly increasing influx of low quality or scam publishers who have embraced open access because it is an easier way to bilk money out of insecure early-career academics.
I will assume, however, that you have already vetted the journal and know that it is a significant and reputable one in your field. Let us also assume that it really is just as you present: the article will still be published in exactly the same way, just not behind a paywall and this will cost you nothing. In that case, the general wisdom is that, all else being equal, an article that's easier to find and read is likely to have higher impact than one hidden behind a paywall.
Free open access in a normally closed journal is actually less unusual than you might think. For example:
The real question is: what is the reason in your particular case? Ask the editor. If it's something that makes sense, like one of the cases above, then great! Embrace it and get some extra citations. If not, then ask yourself again whether you really trust this journal...
