Omnibus structures are efficient and common, especially for non-US intermediaries and introducing brokers. The trade-off is transparency: beneficial ownership sits in the intermediary's books, so identifying the end client requires asking them.
Segregated or fully disclosed accounts reverse the trade-off, giving position-level visibility at the clearing layer and clearer protection in an insolvency, at higher cost.
Example: an intermediary holds 900 clients' positions in a single omnibus account showing a net long of 12,000 contracts. If the intermediary fails, unwinding who owns what depends on its own records, which is slower and riskier for clients than a fully disclosed structure.
Related: clearing-broker, prime-broker, street-name, kyc