Association membership?

The association model is to minimize the cost & time involved in filing in several states. In some cases, the carrier may be given a "pass" on some mandates (but this is rare).

They still have to file policy forms, rates, etc with the DOI before they are allowed to write business in the state. Plans that use the association model are usually allowed to operate in a state (once forms & rates have been submitted for review) under the deemor provisions.
In MD both GR and Assurant offer PPO plans without a copay - Aetna, BX and Coventry do not.

Also, rating is not flexible. Aetna, BX and Coventry have "family rates" regardless of if you have a family of 3 or 8. If you have a family of 3 Aetna and BX are bad deals.

But GR and Assurant only charge per member so smaller families get a better deal.

Also, GR and Assurant can rider conditions - Aetna, BX and Coventry cannot rider therefore reject far more clients.