The challenge for Mercury is that on the surface it doesn't appear they are competitive on rates or fees, so if you are a YC founder and even if no one there is explicitly saying that you must choose a YC-backed company over one that is not when choosing the right tools for your business, there is little other information out there that would sway you to not choose the YC one, especially one in this case that has a big head start. Choosing a tool to handle your money for you takes a lot of trust, and I think a lot of startups would look at the funding, headcount/team, and brand that Brex has built and feel like it would be the far safer option, given what's publicly known. I tried googling reviews for Mercury and the only thing I could find was the Product Hunt listing, which is at 3/5 stars.
The rate comparison is actually pretty big because Mercury is only paying the 1%-1.5% on the savings account (which is frankly an uncommon account to use/need for a business), so you'd have to deal with transferring funds between a checking and savings while adhering to the legal transfer limits, whereas with Brex it's just one interest-bearing cash account paying 1.6%.
Yeah, Mercury's going to have to up their game if they want to stay relevant. I remember my disappointment when I found out I had to park 250k in a 0-yield checking account to qualify for the 1.5% yield on a savings account that can only do something like 5 transfers a month, making it a complete non-starter for running a real business. It felt like they're playing all the same old tricks on us as the incumbent banks, just with a prettier UI.
This new Brex account with 0 fees and 1.6% yield on the entire deposit with no transaction limits feels like a breath of fresh air in comparison.
The rate comparison is actually pretty big because Mercury is only paying the 1%-1.5% on the savings account (which is frankly an uncommon account to use/need for a business), so you'd have to deal with transferring funds between a checking and savings while adhering to the legal transfer limits, whereas with Brex it's just one interest-bearing cash account paying 1.6%.