So 6 digits is low entropy, but it is compensated by a few layers of security. I don't know in practice how effective it is against passwords. I have seen it done in several banks, insurance companies, etc... including online banks. So I guess that it is not that bad. Most discourage SMS/email second factor in favor of their apps though. The physical fob is probably a hassle for them so they will try to push you to other solutions, usually an app.