I haven't done the one-ways to/from the airports so I can't comment on that end, but one issue with pickups in the city is that sometimes the garage doesn't have the car ready when you arrive. You can sometimes call in advance but it's no guarantee. The alternative is to get there early so you don't cut into your (paid) reservation time but I'm pretty sure the car won't work until your reservation begins. So it can be a minor inconvenience and offset any time savings.

The other issue is that if the fuel goes < 1/4 you have to add fuel or there's a penalty charge. Fuel is included and you use a "corporate card" of sorts, but it can be a hassle to have to stop at a gas station.

My concern at the airport end is how convenient the spots are to the terminals. If you have to drop the car off or pick it up at the Hertz rental location, that can add 10 minutes or more to the journey. Hopefully others can chime in with specifics.