Reputation of Frontiers Journals (Received Invitation Chemistry)
In my opinion, Frontiers journals are only modestly predatory. They are clearly for-profit, and seem to have a journal for every sub topic, not to mention the constant invitations for submission and ‘special issue’.  However, they’ve done a pretty good job maintaining reputation, though it certainly differs per-journal. An impact factor of ~3 isn’t that far outside middle-tier, non-profit, established journals. If it helps, I have a publication in the top-tier journal Neuron in 2012 with 156 citations and a pub in Frontiers in 2014 with 120 citations. So worry less about it being ‘frontiers’ and worry more about writing a solid work.