They are regulated by 13 countries: Australia, Belgium, Canada, Hongkong, India, Indonesia, Japan, Malaysia, New Zealand, Singapore, UK, US, UAE. Most EMIs generally regulated by 1 or 2 authorities(also generally in low profile countries). They're the biggest EMI in the world in terms of offices, employees, turnover, customers. Their latest valuation is 5 Billion USD.
As I mentioned before, I'm using TW for more than 3 years and transacted more than $4M without any issues also one of my friends using it and almost transacted the same amount and again zero problems. I mean about $10M transaction without problems since 2017.
Problems can always happen that's why I have a backup business account but this is not specific for Transferwise. Someday TW can close my account and I will switch to the backup account but before that, I will use TW since it is the best IMO. I have a personal bank account with the world's biggest private bank but still, have another good personal bank account to hold money. Always expect, unexpected.
They are good for retail customers, I agree on that. But I would never ever have a business relationship with ignorant companies. Doesn't matter if that's a financial institution, or different kind of business.