Oh yeah I hadn't actually read their submissions page which seems to be where they hide all the small print.
"We offer publication exclusively to the Amazon network."
Not exactly a red flag but not really great either. Staying exclusive with Amazon has lots of benefits for a new author - mainly being that you can put your books in Kindle Unlimited, it's the biggest online retailer with the most traffic and a complex set of algorithms that actually wants to help you sell books, and you only have one customer base to market to (compared with multiple if you choose to 'go wide')
However.
Those same algorithms heavily favour authors who are getting books out every 30 days so it doesn't seem the best choice to put all your eggs in the Amazon basket if you're going the slower trad route.
It seems to me like the advantage of going with a publisher is getting into stores and outlets that just aren't available to most indie (be it self or small press) publishers? I.e if I got an agent I'd want to be in brick & mortar stores, I'd want to be in German, and I'd want them to be selling my audio rights etc.
But I could almost get over that if it wasn't for....
"You are in charge of the marketing and promotion. The process of publication, promotion, and marketing requires an understanding of and experience with social media."
So... they expect you to spend your own money to market your books in return for a fraction of a fraction of royalties 
yep, avoid!!
It seems to me like their business model is based on throwing spaghetti at the wall and hoping some of it sticks. And some of it will stick, of course, because like I said Amazon wants to sell books. Lightning will strike for them every once in a while. They'll also have authors who do spend the money to promote because they want to do well and sell books, so they'll probably make enough to recoup their costs.
But please don't get involved with a 'publishing house' whose model is based on throwing spaghetti at the wall.
ALL THAT SAID
IF they prove to have some benefits that you personally think are important to you, and you couldn't afford yourself, then you might want to consider it a worthwhile sacrifice. For example, I have friends who did a little stint in trad publishing and they said there was one benefit and that was the team of developmental editors, line editors, copy editors etc. They've never replicated that model in their own business because it's a poor return on time / cost investment, but I imagine it's probably really useful to go through that whole process at least once.
Some other benefits might be working with a cover designer (if they allow you to have any input) a copywriter (again, if they have one and allow you to get involved in that process) and to start getting your name out there (although doubtful, just checked a lookinside on Amazon and all links are pointing to them, NOT the author).
I hope that helps in some way. Best of luck with landing an agent 🙏🏻!!