Here's my story. I'm a pretty experienced pistol guy I would say. I shoot practical pistol competitions almost every weekend. I work very part-time facilitating/coordinating a competition league at a local indoor range. I shoot about 1k-1.5k rounds per month.
I was waiting and waiting for a Shield late last year. I knew that's what I wanted since my primary platform is the M&P and I love them. I finally gave up waiting to find one at a decent price and bought a Walther PPS. I shoot it and I love it. It handles really well for a subcompact 9mm. Ergos are fine by me, shoots accurately and more like a bigger gun.
Sure as shit, two weeks after I buy the PPS I get a heads up that Sportsman's in Thornton got a big shipment of them. I went up early the next morning to see if any were left. I bought two since I knew a good friend was looking for one as well.
I took it to the range the day I got it. Shot it side-by-side the PPS. I ended up preferring the PPS so much that I kept it and sold the Shield right away. It wasn't a bad gun at all. In fact, if I had bought it first I would have been just as happy as long as I had never shot a PPS later. lol
The thumb safety is nearly useless. I handled one early last year when they first hit the streets. The thumb safety was not operable by my strong hand thumb. I had to hit it with my weak hand. The one that I bought later on was much better, but still not great. Pretty stiff and not a lot there to get a purchase on. The PPS feels a little bigger and was easier to handle and more comfortable actually, to me.
Would I pay $600 for a Shield? Hard to say. With the current market it's tough to say for sure. How desperate are you to have it or something comparable? Are you interested in anything comparable? Knowing what I do now, I would not. If I were still waiting on one, didn't have the PPS yet, and I had to pay $600 for it? I still doubt it. Merely on principle I'd have a real hard time paying a 35% markup. I know the PPS isn't cheap, but in the end I feel like I made the right choice personally. The other I was strongly considering was the XDs, but I ended up sticking with 9mm. I'd still like to have an XDs as well.
Sorry, that's probably real long. Thought I'd try to give some thorough first hand opinion.