I'm published with two digital first publishers and I assure you there is
nothing hinky going on with them. My Siren-BookStrand titles all went to print as well as being available in e-book format, but that's a matter of company philosophies. And to be honest, the royalties I've received from print books are negligible when compared to the e-books. Readers want the e-books, at least in this genre.
Evernight doesn't send as many titles to print because (a) they don't sell as well as e-books; (b) readers want e-books over print titles.
Yes, there are some questionable digital first publishers out there, but it's not fair to make a global statement that ALL digital first publishers should be avoided. It depends on what you've written, obviously, because most of them are romance publishers. Some also publish other genres but the majority of their sales come from romance novels.
As with any publisher, you want to do your homework first, and ideally speak to their authors. Most have a list of them on their website somewhere, with social media links. Most authors are more than happy to give others the good and the bad about their publisher if asked.
Yes, you can upload books on e-book platforms yourself, but by signing with a publisher I avoid up front costs like covers and editing. My publisher takes care of all that at no cost to me. There are no costs to me, otherwise it would be a vanity publisher, and it's not.
My royalties are much higher than they'd be with traditional print publishers - 45% at Evernight. When you consider what professional editing and decent covers cost, plus buying ISBNs for your books, and paying for formatting unless you can figure it out yourself, to me it's worth having a publisher behind me.
Evernight does a lot of advertising - much more so than Siren. And again, I pay for none of that. I could pay for it on the same sites they do if I wanted, but we're talking hundreds if not thousands of dollars a month. Professional editing costs hundreds up into thousands of dollars per book, depending on the depth of editing you need and how clean the manuscript is to begin with. Covers can make or break a book. Sure, you can do it yourself with any decent photo editing program, but most covers done by the author look like they were done by the author, if you know what I mean. They're not slick and professional looking. Buying stock images to use on them costs money. Investing in the software needed to edit the photos and make the cover - unless you want one that looks REALLY bad - costs money. Some authors get it right, but the majority I see are really bad.
When you take into account all the costs associated with self-publishing, I make more money by taking my 45% royalties from Evernight and letting them do all the work of paying for advertising, paying for fabulous covers, and paying an editor. Not to mention I don't have to mess with formatting or any of that crap, and if a mistake is made (which rarely happens), they fix it, not me.
Digital first publishers like Evernight are recognized as legitimate publishers by the RWA (Romance Writers of America). Trust me when I say that organization will kick a publisher off its list if they start doing anything shady, like not paying their authors on time. Case in point:
http://deirdre.net/rwa-notice-regarding-elloras-cave/
Bottom line: Not ALL digital first publishers are shady. Most are legitimate, royalty paying publishers, and do not charge their authors any hidden or up front costs. If anyone has any questions about Siren-BookStand or Evernight, ask them, or send me a PM if you don't want that question searchable, as this is a public forum.