Also
Not to mention a few of the big boys have "Internet only" brands: First Direct (HSBC), Smile (Co-operative Bank), etc. These typically have their own customer service and distance themselves from their parent operationally, while still leaning on that reputation.
One thing that concerns me about investing in Mondo is that their only fruitful exit strategy might be being bought out. People are notoriously relunctant to switch current accounts, and a bad decade for public faith in banks might mean people will likely stick with names they know.
They're also at least a year from launch afaict, and Android doesn't seem to be a priority. They could miss the boat.