For what it's worth -
Most National renters are existing members that grab and go, the counters are usually very empty. (Talking about Airport/aisle locations).

Even if there is a customer at the counter, National's business model makes transactions go fast.
National agents don't do lengthy upsell (if at all). National renters typically either have Corporate Rates where CDW are included, or they are renting with credit cards with coverage.
There are no early return fees. Rental Rate is pro-rated to the days you have the vehicle only. Less causes of billing disputes at return.

It is just a very different crowd / interactions vs. the stereotypical rental car counter experience.