The Mettle account is an e-money account provided by Prepay Solutions (PPS), a trading name of Prepay Technologies Ltd which is an electronic money institution
Not sure about the “By NatWest” part - it might be endorsed/branded/marketed by them but your money is still in the hands of a third-party e-money institution that looks like it has nothing to do with NatWest and has the potential to go bust (and no FSCS protection as it’s not a bank).
I find their homepage misleading - one of their selling points is “You’ll have confidence knowing we’re part of a trusted and regulated bank.” but yet the actual money is held by a third-party that is independent of NatWest.
Also the account features seem very basic and no desktop/web support. While it’s fine for basic banking I would really prefer if the accounting/invoicing features were available on the web so they can be used from a desktop. I didn’t see a mention of FreeAgent anywhere on the website either. No Apple Pay/Google Pay support either.
As it stands I really don’t see why anyone would go with them instead of Starling Bank (which offers a free business account, web access, mobile payments and FSCS protection). Why would they even launch with such a limited feature set?