Dev crypto done correctly?: check source code. Used publicly used crypto packages too.
Centralised password manager servers vs “dedicated vm” I suppose you mean relay?: 2 layer of encryption, even if their entire VM is hacked, there’s no way to decrypt the data.
Replace you password manager?: it’s your choice, currently all if not all stored and controlled centrally, they can change policy, change billing, change anything they want. Here, it’s running on open protocol.