I linked my banks and credit union to Fidelity the old fashioned way, using trial deposits. But now, they have totally done away with that for new banks / credit unions you may want to add.
You have to use Finicity. There is NO WAY I will give up any financial login credentials to a third party service.
I guess I’m glad I did my linking in the past. If they ever try to force me to use them… it’s totally “see you later Fidelity”. I will not use Finicity, or Plaid, or anything kind of pass-thru that needs my login credentials! These are huge security risk, and invite Scams and Ripoffs!
Alternatively, you may set up an “intermediate” checking or savings account with Fidelity from a credit union WITHOUT any external linked accounts. Then use your other banking accounts to link to this intermediate account for deposit and withdraw money.
Even if the intermediate account is compromised, hackers still can’t gain access to your other assets, since there is no info in it. Transactions are done from either Fidelity or your other banks.
I’m not understanding what this is at all:
“intermediate” checking or savings account with Fidelity from a credit union WITHOUT any external linked accounts
It sounds like Bruce Lee’s "Enter the Dragon art of fighting without fighting. Linking a bank without linking.
Maybe an example is better:
Let’s say you have a savings account in Bank A, and a checking account in Bank B.
From Bank A, the checking account of Bank B is set up as one external transfer account. This will let you move money in and out of Bank B via ACH from Bank A. Don’t set up any external transfer account in Bank B for clarity.
When you log onto Bank B, you can see transactions from Bank A, maybe with four digits of the account # of Bank A. Generally that is not enough to gain access to your Bank A accounts.
The checking account in Bank B is what I meant “intermediate” checking account.
Fidelity can be you your Bank A. From another Bank C you can set up Bank B for external transfer like Bank A. Bank A and C (D,E,..) are where you park your money typically.
In real life, I have my main checking account and main MM account in two credit unions for many years. I pay ebills, write checks with this checking account when I need to. It has just enough money for the checks, and $200+ for a quick unplanned expense. No issue so far.
But if you set up a new Fidelity account today, you can’t do any of this linking of accounts you describe without Finicity. Everything you described would not be possible today in a new fidelity account without giving up your username and password to Internet strangers.
You give up the username and password of Bank B for Finicity.
That’s not good. If someone gets in to Bank B, they could pull money from whatever is linked to that bank, unless I only pull from Fidelity but that is very slow… pulled ACHs take a long, long time to clear. Sometimes weeks. Nah, they messed this one up.
No external transfer account set up in in Bank B. That is the whole point. 
If you really hate it, try to enter the bank info yourself as show below:
