If this were a conventional commercial publisher that was in position to distribute the books widely it would be a very good deal. If it is a purely speculative venture by someone with no previous experience of the book trade, then it is probably not such a good deal.
The deal between a publisher and a writers is based on what each brings to the table, and, like everything else, on scarcity. If the publisher is a major publishing house with an established reputation and distribution network, they bring a lot more to the deal than if it is someone outside the industry deciding to dabble for the first time. In other words, the experienced commercial publisher can sell a whole lot more books than the newcomer, which means they are offering the writer a much bigger paycheck, even if they are offering a lower cut on a per book basis.
What you as a writer should care about are:
How much am I getting paid overall.
How much exposure am I getting (both because we write to be read and because the more exposure we get, the more books we sell).
A publisher who can't demonstrate the ability to sell a lot of books and get you a lot of exposure is therefore bringing less to the table and so needs to offer you a bigger cut of the sales they do make for it to constitute a good deal.
Of course, it also depends on who else they can get to do the writing for them. There are many willing writers but few able ones. If they think you are one of the able ones, they should be willing to pay for that. (And if they are not, it means they don't think you are one of the able ones, or they can't tell the difference (or you are not one of the able ones).) Deals for the willing but not able are too low to live on, but people will still snap them up, so you just have to decide what you are willing to settle for.