I have published a paper in a then new journal about 2 years ago. As my paper is one of their most cited so far, they have since invited me to publish another article (fully open access, waiving the APCs) last year. I took the offer and published another paper there (the BA thesis results of a student I suupervised). As this paper was also well received, they have extended another invitation to publish a paper, again OA and with waived APCs. As this is new (now about 2 years old), it does not have an impact factor nor does it appear in any journal rankings, yet with a reputable publisher.
I do have some results from my PhD research that I plan on publishing in the near future. I now wonder if I should take them again up on their offer, as it makes things considerably easier - the scope fits, and there is no cost (my uni also has an open access fund, but it is not limitless and the portion I would not use could benefit others without the possibility of cost-free publication). Other, more established journals (with impact factors) on the other hand would probably look better on a CV, or wouldn't they? But then again, if many high quality papers will be published in the new journal, it will get more recognition and by the time it will be of importance to me, the journal might get listed in rankings and will be positively viewed. After all, if everyone takes their good papers only to the established journals, newer journals do not really have a chance to rise. Then again, publishing many papers at just one journal may be perceived as being lazy or unambitious (I don't really know if that is the case).
So I guess my question is, is it a bad idea (academic career-wise) to publish for free at not yet established journals (especially as a PhD student)?