This is my understanding too. When I’ve discussed this with Jonas (Monzo CTO) he said that Monzo doesn’t want to charge fees because “it’s very hard for banks to compete with free”. In other words, if Monzo did charge fees then the banks would be able to undercut Monzo by charging a lower fee.
Since Monzo has a much lower overheads (no branches or legacy infrastructure to maintain), it can afford not to charge fees & as Josh mentioned, it will make it’s revenue by offering overdrafts (obviously users will be able to choose whether or not request an overdraft). Tom has said that Monzo should break even next year, after the overdraft product is launched.