I've started doing that with my Merrill CMA Edge account, just the money market it does the automatic cash sweep into only pays 0.04% interest, so I have to manually buy/sell in in and out of higher yeild money market funds that are avaialbe through it, some yeild >5% though.
It is also my brokerage account, so no having to transfer money between my "checking" and brokerage accounts.
I've had a little difficulty getting a couple things to debit from it for payments, as their systems don't see a "checking" account when I try to link to it via plaid, even though it has a checking account routing and account number, and I have regular checks for it.
@kremonis wrote:I recently open a MMA that I really like and want to make it my hub/bill pay account.
Assume this MMA does not have a 6 times a month withdrawal limitation.
Are there any pitfalls or limitations in general about using an MMA has a hub
account to pay bills, push and pulls ACHs?
The lines are becoming blurred between checking, savings, MM-checking, MM-savings,
investment checking, brokerage gateway, etc.
The bottom line is that all have limits that are not advertised.
Number of accounts than can be linked.
Number of outgoing transfers (day/week/month).
Push & pull limits (day/week/month).
Speed of ACH transfers.
Interest on money sitting in account.
Minimum funds needed, debit card, checks, bill-pay, extra fee's, etc.
A local CU that will let one link 3 institutions and has an ACH limit of 10k
with 2-3 day ACH average time could be considered a hub account for one person.
.and.
Someone else needs 18 institutions linked, minimum 150k a day transfer limit,
with next day ACH average time.
We don't know your needs or the account limitations.
It might work just fine, and it might not.
Just like the suggestions from other post.
What works for them might not for you
With out a lot of info on what you consider a "Hub" account,
it is very hard to recommend anything.
However as an answer to your origional question.
Yes : Most MM-Accounts usually have more restrictions than checking accounts.
However the restrictions might not limit it for your needs. 
I forgot one potentially useful feature of the Merrill CMA Edge account.
They give you a "deferred" debit card that settles up debit card transactions once a month instead of right away.
While I've not tested it, I believe it counts the "margin balance available for withdrawl" on the account, and not just the cash balance, when approving debit card transactions.
Means you can make a large purchase/payment somewhere with the debit card, even if you don't actually have the cash balance available for it, and will have some time to make the cash available.
