Like the ones discussed in the article, Mercury also keeps customer funds in Evolve, among other banks (I guess they claim to spread your money around so you don't have more thank 250K in any one basket). So if I understand correctly, the problem is that I have no visibility to the back end, so if Mercury keels over I'll have trouble getting my money?
* I used SVB for 25 years, but over the past few years their service declined and First Republic poached a lot of their good guys, so I switched to FRB. With a track record like that, perhaps Mercury should reject me?