Update
I'm on day three of my car rental. here's some observations:
The booking through Hertz from overseas does little; once at the PVG car rental place (there's a shuttle service, pick-up at PVG T2, P2, H6), you basically go through the whole rental process from scratch. Anything already provided in the Hertz reservation is redone, incl. the car. The price at least was 'kept' although my rental is 30RMB more, they say they'll reimburse that on car rental return. Whatever!
They make you download their app, and payment is through that (Alipay/WeChat, UnionPay, etc.). Overall it took a LONG time because of various issues; I spent 90 minutes at the rental car location before being able to drive off.

It worked out okay for me, as I needed to be at a far-away location the next morning, but I'd not go through hertz again; there is just no advantage and it's not easier.

Driving 'conditions':
Since you need a Chinese driving license everyone is already familiar with the 'challenges' in driving in China. I'd say if most of your experiences are from 15, 10 or even 5 years ago, it's IMPROVED immensely since then. The speed cameras, and other traffic controls; the road infrastructure improvements, and the general on-road behavior is a far cry from only just a few years ago.(Caveat: this improved behavior excludes dump trucks, and Audi's without license plates...those two groups are still.... "special"!
The GPS software is also vastly better than it used to be, and even my simple English language apps (Sygic and Maps.me) worked very well. I'd use Baidu maps as it's probably the most accurate, but dang it's just way too bloated. I like the simpler look of the ones I mentioned, despite them not having the most up-to-date maps.


Summary:
Would I do it again: yes, but not through Hertz; I'd just use the Chinese app.

(P.S. I checked out 1hai.cn, but couldn't find a rental location at PVG, only in Shanghai itself.)