I've worked for
FMO's, Brokerage houses, insurance companies and as a captive and independent agent so maybe I can add some insight.
If you are an independent agent I think you need both an
FMO and a primary carrier and here's why. As has been noted the
FMO will always try to pay you as little as possible on your business because they get paid on the spread. Typically this will be 30-40% override but independnet agents need to remember that the payout to the
FMO is loosely based upon the FMOs total premium with that carrier that drives their contract so you aren't giving up 30-40%. You might not even be giving up anything if you don't do a great deal of business.
With your primary company, and there are a good number you can go directly to and who will work with you almost as though you are a captive agent but you're not. You can build a relationship with the key people who help drive your business, the underwriters and case managers etc and you can focus your business and service on that particular company or companies.
As most of these types of companies will pay you directly you will tend to make much more money over time while still retaining the
FMO relationship for those cases thaty don't fit or need more competitive underwriting etc.
I have a main carrier that gets the majority of my business and I have an
FMO relationship where I can shop those cases that need it. I make more, I'm more efficient so clients get better service and everyone is happier.