This is deceitful, it wastes your time as well as the broker's, and it is unnecessary. There is nothing wrong with shopping brokers, but after selecting one you should stick with that broker. If that broker fails to provide adequate service, you terminate the relationship and start anew with another broker. Consumers dealing with MBs don't know the broker's fee until after an application is submitted, which provides some excuse for submitting multiple applications. But consumers dealing with UMBs know the broker's fee upfront, and therefore have no reason to practice this deceit.
Upfront consumers meet their obligation under a rate lock.
When a lender locks the loan, both parties are committed. The lender is committed to delivering the loan even if interest rates jump. The borrower is committed even if rates drop. A float-down will cost a little more. The Mortgage Professor cannot warrant the quality of service provided, or the reasonableness of the prices charged, by UMBs.