Here’s a pretty big one, from their website
The Prepaid Card is an electronic money product and although it is a product regulated by the Financial Conduct Authority, it is not covered by the Financial Services Compensation Scheme. No other compensation scheme exists to cover losses claimed in connection with the Prepaid Card. This means that in the event that Wirecard Card Solutions Ltd becomes insolvent your funds may become valueless and unusable and as a result you may lose your money.
I’m guessing that there’s also a limit to how much they can take in deposits too / what they can do with that money, due to regulations.
I was actually going to point out that being tied to Wirecard doesn’t seem to be a particularly good thing. Following your point, they appear to be the best processor for startups.
But we’ve seen the issues that Monzo’s had because of them (the minimum wait of 3-4 months to enable Apple Pay, as one example & outages as another) so once Monzo is no longer using their services, there should be a lot of benefits.